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Biomedical subjects

M R Bennett

Publications and source records attributed to M R Bennett.

294 records · Page 17Linked to original sources
PubMed1966

Application of the sucrose-gap method to determine the ionic basis of the membrane potential of smooth muscle.

1. A study has been made of the ionic basis of the smooth muscle membrane potential by changing the ionic environment of the ureter and recording the resultant potential changes with the sucrose gap. The relation of these potential changes to the membrane potential of individual cells has also been studied.2. It is shown that if the ionic environment of all the cells in the tissue is uniformly changed, then the potential change recorded by the sucrose gap is proportional to the magnitude of the short circuit factor, the liquid junction potential change at the sucrose-test solution interface, and the amplitude of the membrane potential change of a single cell.3. A simple method is described for determining the steady value of the short circuiting factor, and the liquid junction potential changes, so that the recorded potentials can be corrected to give membrane potentials.4. The action of isotonic potassium sulphate and isotonic potassium chloride on the membrane potentials of the ureter smooth muscle cells is described.5. When the extracellular potassium concentration is changed reciprocally with the extracellular chloride concentration in order to maintain these ions in a Donnan equilibrium across the muscle cell membrane, the membrane potential is found to decrease by 53 mV for a 10-fold change in external potassium concentration, for concentrations above 10 mM.6. It is concluded that above an external potassium concentration of 10 mM the membrane potential of ureteral smooth muscle cells obeys the prediction of the Nernst equation for a potassium electrode.

Cell Membrane↗
PubMed1966

Rebound excitation of the smooth muscle cells of the guinea-pig taenia coli after stimulation of intramural inhibitory nerves.

1. A study has been made of the increase in the rate of action potential firing in spontaneously active cells and of the initiation of action potential firing in quiescent cells of the taenia coli after stimulation of the intramural inhibitory nerves.2. In the majority of cells which fired action potentials spontaneously at intervals of about 1 sec, stimulation of the intramural inhibitory nerves with single pulses gave an inhibitory junction potential (I.J.P.) which was followed by action potentials which occurred at intervals as small as 0.5 sec. The increased rate of firing lasted up to 30 sec.3. A small number of cells were either not spontaneously active or only fired action potentials at intervals greater than 5 sec. After stimulation of the intramural inhibitory nerves with either single or repetitive pulses, the quiescent cells gave I.J.P.S which were followed by either a single action potential or a burst of action potentials.4. The rate of firing of action potentials after an I.J.P., and the duration of this enhanced rate of firing increased with an increase in the mean amplitude of the hyperpolarization during the I.J.P. As the amplitude of the I.J.P. increases with an increase in frequency of stimulation of the nerves, the rebound excitation increases with an increase in the frequency of stimulation of the inhibitory nerves.

Animals↗
PubMed1966

Transmission from intramural excitatory nerves to the smooth muscle cells of the guinea-pig taenia coli.

1. A study has been made of transmission from intramural excitatory nerves to the smooth muscle cells of the guinea-pig taenia coli.2. Only ten cells out of eighty gave depolarizing (i.e. excitatory junction potentials, E.J.P.S) on stimulating the intramural nerves, the remaining cells gave hyperpolarizing responses (i.e. inhibitory junction potentials, I.J.P.S). E.J.P.S were recorded in cells which were less than 1 mm away from cells which gave I.J.P.S.3. In some cells stimulation of the intramural nerves with single pulses of maximal strength gave E.J.P.S of about 20 mV amplitude after a latency of 100-200 msec. In quiescent cells these E.J.P.S gave rise to action potentials. Repetitive stimulation above 1 c/s depolarized the membrane for less than about 1 sec, and during the remainder of the stimulation no action potentials fired, even in spontaneous cells.4. In some cells stimulation of the intramural nerves gave an I.J.P. The largest sized I.J.P.S were generally only about half the size of the I.J.P.S recorded in atropinized preparations. The decreased amplitude of the I.J.P.S enabled rebound action potentials to be fired by successive I.J.P.S when the intramural nerves were stimulated at about 1 c/s. At higher frequencies all spontaneous activity was suppressed.5. The effect of neostigmine (10(-9)-10(-7) g/ml.) on the transmission was studied. There was no detectable increase in the number of cells giving E.J.P. responses in the presence of neostigmine.6. The electrophysiological characteristics of intramural excitatory and inhibitory nerve transmission are discussed.

Animals↗
PubMed1966

An analysis of the transmission of excitation from autonomic nerves to smooth muscle.

1. An analysis has been made of the transmission of excitation from the hypogastric nerve to the smooth muscle cells of the guinea-pig vas deferens.2. Depolarization of single muscle cells with current pulses from an intracellular electrode gave local depolarizations of the cell membrane which were not propagated. The total membrane resistance after 100 msec of depolarization was 15 MOmega for depolarizations between 10 and 40 mV.3. Depolarization of some cell membranes with a current pulse during the excitatory junction potential (E.J.P.) decreased the amplitude of the E.J.P. from about 10 mV at 20 mV depolarization, to nearly zero at 60 mV depolarization. In some cells the E.J.P. was unchanged during depolarizations of 50 mV.4. The action of transmitter on the smooth muscle cell membrane continued for the duration of the E.J.P. Action potentials which occurred at various times during the E.J.P. failed to remove the remaining phases of the E.J.P.5. It was shown that the slow time course of the E.J.P. could not be due to the instantaneous and simultaneous release of transmitter from a number of relatively distant sources.6. It was shown that each smooth muscle cell was innervated by several axons. The serial sections examined with the electron microscope showed that a smooth muscle had either a single axon terminating within 200 A of the muscle or no axons terminating on it at all. Therefore transmitter must be released along the length of the axons as well as at the terminations of the axons.

Animals↗