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M E Krouse

Publications and source records attributed to M E Krouse.

28 records · Page 2Linked to original sources
PubMed1991

Peptide cotransmitter potentiates calcium channel activity in crayfish skeletal muscle.

The activity of 2 types of Ca2+ channels (38 and 14 pS in 137 mM Ba2+) in the plasma membrane of the crayfish tonic flexor muscle is modulated by the peptide proctolin. This peptide serves as a cotransmitter in 3 of the 5 excitatory tonic flexor motoneurons and greatly enhances tension after depolarization by the conventional neurotransmitter. Proctolin alone has no effect on these channels, but renders them capable of sustained activity following depolarization. After depolarization induces activity, 5 x 10(-9) M proctolin increases the open probability of the larger channel up to 50-fold due to a marked decrease in the mean channel closed time. There is also at least a 4-fold increase in the percentage of patches with active channels for the large channel and a 2-fold increase for the small channel. Proctolin modulation appears to occur via an intracellular messenger, possibly cAMP. The peptide's effect on channel activity is dose dependent in a manner that parallels its effect on tension. These results indicate that the activation of these channels and the resulting influx of Ca2+ into the muscle fiber play a role in the potentiation of tension in this muscle.

Animals↗
PubMed1989

Patch-clamp study of cultured human sweat duct cells: amiloride-blockable Na+ channel.

The reabsorptive duct of the eccrine sweat gland has a large transepithelial conductance consisting mainly of a high conductance to Cl- and a smaller, amiloride-blockable Na+ conductance (Bijman and Frömter 1986; Quinton 1986). Cells have been cultured from sweat ducts and their properties previously studied in Ussing chambers (Pedersen 1988) and with microelectrodes (Jones et al. 1988). We have now studied the ion channels present in excised, inside-out patches of human cultured sweat duct cells, and find a marked predominance of linear, 15 pS, amiloride-blockable, low selectivity, Na+ channels. Such channels were seen in 54/92 (59%) of the patches, with up to 7 channels recorded in a single patch. Other channel types were seen at much lower densities. The prevalence of an amiloride-blockable Na+ channel in cultured duct cells clearly distinguishes these cells from cultured sweat gland secretory cells, which lack such a channel.

Amiloride↗
PubMed1989

Ion channels in normal human and cystic fibrosis sweat gland cells.

Single-channel patch-clamp techniques were used to study the population of apical membrane ion channels in cultured sweat gland secretory cells from normal and cystic fibrosis subjects. Four types of anion channels and two types of cation channels were found. At physiological voltages, anion channels had chord conductances of 10, 18, 24, and greater than 200 pS. All had linear current-voltage relations except the 24 pS channel, which showed outward rectification. Cation channels had chord conductances of 5 and 18 pS, were linear, and were nonselective for a variety of cations. Channel types and proportions were equivalent in control, cystic fibrosis, and cystic fibrosis heterozygote cells. Beyond showing that the distribution of channel types remains unchanged in cystic fibrosis cells, the data provide a basis for comparison with cells cultured under different conditions, with other cell types, and with native tissues.

Adolescent↗
PubMed1985

Rates and equilibria for a photoisomerizable antagonist at the acetylcholine receptor of Electrophorus electroplaques.

Voltage-jump and light-flash experiments have been performed on isolated Electrophorus electroplaques exposed simultaneously to nicotinic agonists and to the photoisomerizable compound 2,2'-bis-[alpha-(trimethylammonium)methyl]-azobenzene (2BQ). Dose-response curves are shifted to the right in a nearly parallel fashion by 2BQ, which suggests competitive antagonism; dose-ratio analyses show apparent dissociation constants of 0.3 and 1 microM for the cis and trans isomers, respectively. Flash-induced trans----cis concentration jumps produce the expected decrease in agonist-induced conductance; the time constant is several tens of milliseconds. From the concentration dependence of these rates, we conclude that the association and dissociation rate constants for the cis-2BQ-receptor binding are approximately 10(8) M-1 s-1 and 60 s-1 at 20 degrees C; the Q10 is 3. Flash-induced cis----trans photoisomerizations produce molecular rearrangements of the ligand-receptor complex, but the resulting relaxations probably reflect the kinetics of buffered diffusion rather than of the interaction between trans-2BQ and the receptor. Antagonists seem to bind about an order of magnitude more slowly than agonists at nicotinic receptors.

Animals↗
PubMed1980

A covalently bound photoisomerizable agonist: comparison with reversibly bound agonists at Electrophorus electroplaques.

After disulphide bonds are reduced with dithiothreitol, trans-3- (alpha-bromomethyl)-3'-[alpha- (trimethylammonium)methyl]azobenzene (trans-QBr) alkylates a sulfhydryl group on receptors. The membrane conductance induced by this "tethered agonist" shares many properties with that induced by reversible agonists. Equilibrium conductance increases as the membrane potential is made more negative; the voltage sensitivity resembles that seen with 50 [mu]M carbachol. Voltage- jump relaxations follow an exponential time-course; the rate constants are about twice as large as those seen with 50 muM carbachol and have the same voltage and temperature sensitivity. With reversible agonists, the rate of channel opening increases with the frequency of agonist-receptor collisions: with tethered trans-Qbr, this rate depends only on intramolecular events. In comparison to the conductance induced by reversible agonists, the QBr-induced conductance is at least 10-fold less sensitive to competitive blockade by tubocurarine and roughly as sensitive to "open-channel blockade" bu QX-222. Light-flash experiments with tethered QBr resemble those with the reversible photoisomerizable agonist, 3,3',bis-[alpha-(trimethylammonium)methyl]azobenzene (Bis-Q): the conductance is increased by cis {arrow} trans photoisomerizations and decreased by trans {arrow} cis photoisomerizations. As with Bis-Q, ligh-flash relaxations have the same rate constant as voltage-jump relaxations. Receptors with tethered trans isomer. By comparing the agonist-induced conductance with the cis/tans ratio, we conclude that each channel's activation is determined by the configuration of a single tethered QBr molecule. The QBr-induced conductance shows slow decreases (time constant, several hundred milliseconds), which can be partially reversed by flashes. The similarities suggest that the same rate-limiting step governs the opening and closing of channels for both reversible and tethered agonists. Therefore, this step is probably not the initial encounter between agonist and receptor molecules.

Animals↗
PubMed1978

Response of acetylcholine receptors to photoisomerizations of bound agonist molecules.

In these experiments, agonist-induced conductance is measured while a sudden perturbation is produced at the agonist-receptor binding site. A voltage-clamped Electrophorus electroplaque is exposed to trans-Bis-Q, a potent agonist. Some channels are open; these receptors have bound agonist molecules. A light flash isomerizes 3(-35)% of the trans-Bis-Q molecules to their cis form, a far poorer agonist. This causes a rapid decrease of membrane conductance (phase 1), followed by a slower increase (phase 2). Phase 1 has the amplitude and wavelength dependence expected if the channel closes within 100 mus after a single bound trans-Bis-Q is isomerized, and if the photochemistry of bound Bis-Q resembles that in solution. Therefore, the receptor channel responds rapidly, and with a hundred-fold greater closing rate, after this change in the structure of a bound ligand. Phase 2 (the conductance increase) seems to represent the relaxation back toward equilibrium after phase 1, because (a) phase 2 has the same time constant (1(-5) ms) as a voltage- or concentration-jump relaxation under identical conditions; and (b) phase 2 is smaller if the flash has led to a net decrease in (trans-Bis-Q). Still slower signals follow: phase 3, a decrease of conductance (time constant 5(-10 ms); and phase 4, an equal and opposite increase (several seconds). Phase 3 is abolished by curare and does not depend on the history of the membrane voltage. We consider several mechanisms for phases 3 and 4.

Animals↗
PubMedDate not supplied

A large anion-selective channel has seven conductance levels.

Ion channels have generally been found to have two predominant conductance levels thought to be associated with 'open' and 'closed' states, but intermediate (subconductance) states have also been reported. We have now found that a large conductance, anion-selective channel in pulmonary alveolar epithelial cells can adopt any of six open levels of conductance that are integer multiples of 60-70 pS. The channel is usually either fully open or fully closed. The frequencies of the different conductance levels are inconsistent with the notion that there are six independent channels. We suggest that the channel consists of six conducting pathways in parallel, 'co-channels', with a shared gating mechanism that can synchronously render all of them non-conducting. Other channels with lower maximum conductance may operate in a similar way but multiple conductance levels would not easily be detected because of a less favourable signal-to-noise ratio.

Anions↗