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Biomedical subjects

M A Werz

Publications and source records attributed to M A Werz.

9 recordsLinked to original sources
PubMed1987

Dual actions of phorbol esters to decrease calcium and potassium conductances of mouse neurons.

Phorbol esters, which substitute for diacylglycerol to activate protein kinase C, were applied to mouse dorsal root ganglion and cerebral hemisphere neurons in cell culture. The phorbol esters, phorbol 12,13-dibutyrate and 12-O-tetradecanoyl-phorbol-13-acetate, prolonged calcium-dependent action potential duration at resting membrane potential and at more negative membrane potentials but decreased action potential duration following membrane depolarization to less than -45 mV. When calcium and potassium currents were recorded using the single electrode voltage-clamp technique, the phorbol esters were shown to reduce both voltage-dependent calcium and potassium currents. These studies have demonstrated directly that phorbol esters, presumably by activating protein kinase C, can modify more than one membrane conductance in individual neurons.

Animals↗
PubMed1987

Forskolin and phorbol esters reduce the same potassium conductance of mouse neurons in culture.

Second messenger systems may modulate neuronal activity through protein phosphorylation. However, interactions between two major second messenger pathways, the cyclic AMP and phosphatidylinositol systems, are not well understood. The effects of activators of cyclic AMP-dependent protein kinase and protein kinase C on resting membrane properties, action potentials, and currents recorded from mouse dorsal root ganglion neurons and cerebral hemisphere neurons grown in primary dissociated cell culture were investigated. Neither forskolin (FOR) nor phorbol 12,13-dibutyrate (PDBu) altered resting membrane properties but both increased the duration of calcium-dependent action potentials in both central and peripheral neurons. By means of the single-electrode voltage clamp technique, FOR and PDBu were shown to decrease the same voltage-dependent potassium conductance. This suggests that two independent second messenger systems may affect the same potassium conductance.

Action Potentials↗
PubMed1987

Actions of mu, delta and kappa opioid agonists and antagonists on mouse primary afferent neurons in culture.

The effects of selective mu, delta and kappa opioid agonists and antagonists were studied on somatic calcium-dependent action potentials recorded from mouse dorsal root ganglion (DRG) neurons grown in dissociated cell culture. The mu selective agonist, PL 017, and the delta selective agonist, [D-Pen2, L-Pen5] enkephalin (DPLPE), reduced action potential duration of a subpopulation (21/56) of DRG neurons. Leucine-enkephalin reduced action potential duration of all neurons sensitive to PL 017 or DPLPE, whereas 85% of neurons responding to leucine-enkephalin responded to either PL 017 or DPLPE. Only 15% of neurons responded to both PL 017 and DPLPE. There was no significant difference in the response to PL 017 or DPLPE when compared to leucine-enkephalin. In another experiment, the kappa selective agonist dynorphin A (DYN A), PL 017 and DPLPE reduced action potential duration of a subpopulation (15/67) of DRG neurons. There was a heterogeneous response among neurons to PL 017, DPLPE and DYN A inasmuch as 21.4% of neurons responded to all three agonists, 35.7% responded to PL 017 and DYN A, 35.7% responded only to PL 017 and 7.1% responded only to DYN A. Responses to the mu selective agonist PL 017 were antagonized by the reversible opioid antagonist naloxone and the selective mu antagonist SMS 201-995 in a concentration-dependent fashion. Responses to PL 017 were not altered by the selective delta antagonist ICI 174864. Responses to PL 017 were reduced by the irreversible, selective mu antagonists beta-funaltrexamine and naloxonazine in a concentration-dependent fashion.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1987

Phorbol esters: voltage-dependent effects on calcium-dependent action potentials of mouse central and peripheral neurons in cell culture.

The beta-phorbol esters 12-O-tetradecanoylphorbol-13-acetate (TPA) and phorbol 12,13-dibutyrate (PDBu), which activate protein kinase C, were applied to mouse dorsal root ganglion (DRG) and cerebral hemisphere neurons grown in primary dissociated cell culture. Phorbol esters did not modify the membrane potential or input resistance of either type of neuron. To assess the effects of beta-phorbol esters on voltage-dependent conductances, the effects of PDBu and TPA on action potentials evoked from these neurons were determined. The neurons were bathed in a solution containing 5 mM tetraethylammonium and action potentials that contained sodium and calcium components were evoked. When applied at resting membrane potential and at more negative potentials, PDBu and TPA reversibly increased action potential duration. The alpha-phorbol ester 4-alpha-phorbol, which does not activate protein kinase C, did not modify action potential duration. The effects of the beta-phorbol esters, however, were voltage-dependent. When the neurons were depolarized to membrane potentials less negative than -50 mV, PDBu and TPA reduced action potential duration. The effects of both PDBu (10 nM-1 microM) and TPA (100 pM-100 nM) on action potential duration were dose-dependent. The prolongation of action potentials produced at large negative potentials may be due to a reduction in voltage-and/or calcium-dependent potassium conductance, since the prolongation was associated with a reduction in the potassium-dependent afterhyperpolarization; following membrane depolarization in control solution, action potential duration was increased for several minutes, while the afterhyperpolarization was reduced and, following this prolongation, phorbol esters no longer prolonged the action potentials.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1986

Adenosine agonists reduce voltage-dependent calcium conductance of mouse sensory neurones in cell culture.

Adenosine and several of its analogues produced a concentration-dependent shortening of calcium-dependent action potential (c.a.p.) duration of mouse dorsal root ganglion (d.r.g.) neurones in dissociated cell culture. The following rank order of potency was obtained: N6-(L-phenylisopropyl)adenosine greater than N6-(D-phenylisopropyl)adenosine greater than N6-cyclohexyladenosine greater than 2-chloroadenosine much greater than 1-methylisoguanosine greater than adenosine. Effects of adenosine agonists on c.a.p. duration were blocked by methylxanthine adenosine antagonists. Adenosine monophosphate (AMP) and cyclic AMP shortened c.a.p.s in d.r.g. neurones, while ATP also depolarized cells. Voltage-clamp analysis revealed that the effect arose from reduction of a voltage-dependent calcium conductance. Adenosine agonists reduced depolarization-evoked inward currents but did not alter membrane conductance following blockade of calcium channels by cadmium. Additionally, adenosine reduced the instantaneous current-voltage slope (chord conductance) during step commands that produced maximal activation of voltage-dependent calcium conductance. If effects of adenosine on neuronal somata and synaptic terminals are similar, adenosine agonists may inhibit neurotransmitter release in the central nervous system by inhibiting a voltage-dependent calcium conductance. Since effects of adenosine agonists did not correspond with their relative potencies as modulators of adenylate cyclase activity or inhibitors of neurotransmitter release in peripheral tissues, a novel adenosine receptor may be involved in regulation of this conductance.

Action Potentials↗
PubMed1986

Dynorphin A decreases voltage-dependent calcium conductance of mouse dorsal root ganglion neurones.

The actions of the opioid peptides dynorphin A and (Leu)enkephalin were assessed on calcium-dependent action potentials and inward calcium currents recorded from somata of mouse dorsal root ganglion (d.r.g.) neurones grown in primary dissociated cell culture. Dynorphin A and (Leu)enkephalin decreased the duration of somatic calcium-dependent action potentials in a portion of d.r.g. neurones impaled with potassium acetate-filled micropipettes. When substantial potassium conductance was blocked by intracellular injection of caesium acetate, d.r.g. neurones continued to respond to dynorphin A but responses to (Leu)enkephalin were abolished. In voltage-clamp experiments, dynorphin A but not (Leu)enkephalin reduced the magnitude of inward calcium currents. Dynorphin A responses were blocked by the opiate antagonist naloxone. The dynorphin A effect was due to reduction of voltage-dependent calcium conductance since dynorphin A reduced depolarization-evoked inward currents but did not alter membrane conductance following blockade of calcium channels by cadmium, and because dynorphin A reduced the instantaneous current-voltage slope (chord conductance) during step commands that produced maximal activation of voltage-dependent calcium conductance. Dynorphin A binds with high affinity to kappa-opioid receptors. (Leu)enkephalin, which has affinity for both mu- and delta-receptors but not for kappa-opioid receptors, was without effect on calcium conductance. Therefore, we suggest that kappa-receptors are coupled to voltage-dependent calcium-channels and that binding of dynorphin A produces a decrease of calcium current.

Action Potentials↗
PubMed1985

Dynorphin and neoendorphin peptides decrease dorsal root ganglion neuron calcium-dependent action potential duration.

Opioid peptides decrease somatic calcium-dependent action potential duration of a subpopulation of mouse dorsal root ganglion (DRG) neurons grown in dissociated cell culture. Based on rank order of potency and naloxone sensitivity, both mu and delta opioid receptors were demonstrated on the somata of DRG neurons and were shown to have a heterogeneous distribution. The purpose of the present investigation was to determine the actions of dynorphin gene products, dynorphin A, dynorphin B, dynorphin A(1-8), dynorphin A(1-9), alpha-neoendorphin and beta-neoendorphin on DRG neuron somatic calcium-dependent action potentials and to compare the actions of dynorphin and neoendorphin peptides to the action of morphiceptin, a mu receptor-selective ligand, and Leu-enkephalin, a delta receptor-preferring ligand. We report that the dynorphin and neoendorphin peptides decreased DRG neuron somatic calcium-dependent action potential duration in a portion of DRG neurons, an action that was dose-dependent and was antagonized by naloxone. DRG neuron responses to the dynorphins and neoendorphins differed from responses to morphiceptin and Leu-enkephalin. First, many DRG neurons responded to dynorphin A but not to morphiceptin or Leu-enkephalin. Second, dynorphin A responses, unlike responses to morphiceptin or Leu-enkephalin, were present after intracellular injection of cesium, a potassium channel blocker. Dynorphin A effectiveness was decreased after deletions at the carboxy-terminus and Leu-enkephalin [dynorphin A(1-5)] was inactive at 10 microM. Thus, on DRG neurons in cell culture, dynorphins and neoendorphins act at opioid receptors distinct from mu and delta receptors, possibly kappa receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1985

Barbiturates decrease voltage-dependent calcium conductance of mouse neurons in dissociated cell culture.

Barbiturates have been shown to reduce presynaptic release of neurotransmitter. It is likely that barbiturates alter transmitter release by decreasing calcium entry since barbiturates decrease calcium influx into synaptosomes and reduce the maximal rate of rise and duration of calcium-dependent action potentials. The mechanisms of barbiturate action on neuronal calcium entry have been studied using mouse dorsal root ganglion neurons in cell culture. Dorsal root ganglion neuron action potentials have a calcium-dependent component which is decreased by the barbiturates, pentobarbital (50-500 microM) and phenobarbital (500-2000 microM). Calcium-dependent action potential after hyperpolarization was also decreased by barbiturates. Intracellular injection of the potassium channel blocker, cesium, enhanced barbiturate actions. In voltage-clamp studies, barbiturates reduced inward calcium current and calcium chord conductance without altering the leak conductance which is present after all calcium conductance was blocked by application of cadmium ions (100 microM). Calcium current inactivation was accelerated by barbiturates but unaffected by cadmium. We conclude that barbiturates reduce calcium conductance by enhancing calcium channel inactivation or by producing open channel block of calcium channels.

Action Potentials↗