Appearance Of Action Potentials Research Articles

Electrophysiology of mammalian gland cells.

The resting cell membrane potential varies from -40 to -70 mV according to type of gland cell and species. The RP depends mainly on the large transmembrane concentration gradient for K maintained by a pump mechanism extruding Na and accumulating K. Since the Na permeability (PNa) is much smaller than PK, the Na concentration gradient is less important. In addition to the dominant electrodiffusional control of RP the Na pump itself contributes since the active transport of Na (out) exceeds that of the active K uptake. Gland cells are generally electrically coupled--i.e., the junctional membrane resistance is much lower than the surface membrane resistance. The coupling may be widespread (e.g., liver) or confined to one acinus (e.g., salivary gland and pancreas). The specific surface cell membrane resistance may be about 2000 omega cm2. A number of neurotransmitters and hormones control cellular transport processes by their action on surface cell membrane receptors. Agonist-receptor interaction causes prominent changes in membrane potential and resistance, in many cases of a complex nature. Most gland cell membranes so far investigated in detail appear to be electrically inexcitable; i.e., stimulation does not cause the appearance of action potentials (e.g., salivary glands, exocrine pancreas, and liver) but prominent exceptions to this are the endocrine pancreas (beta-cells) and the adrenal cortex. The main importance of agonist-induced membrane permeability changes is to alter the intracellular ion activities. An increase in [Na+] seems to be important whenever stimulation results in fluid transport and an increase in [Ca2+] triggers exocytosis.

Electrical and mechanical activity of the longitudinal muscle of the anterior mesenteric artery of the domestic fowl.

1. The electrical activity and changes in tension of the longitudinal muscle of the anterior mesenteric artery (LMAMA) of the domestic fowl were recorded simultaneously using the sucrose-gap method.2. Spontaneous activity consisted of recurring contractions each accompanied by a burst of action potentials.3. In quiescent preparations, brief electrical stimuli, acetylcholine, or barium chloride produced contractions with the appearance of action potentials. Larger concentrations of barium chloride or acetylcholine produced depolarization and action potentials ceased although contraction was maintained. Whenever depolarization without action potentials occurred, it was associated with a smooth contraction, whereas action potentials were always accompanied by small rapid contractions super-imposed upon the main contraction.4. When the tone was raised with barium chloride (and in the presence of hyoscine) continuous action potentials occurred; under these circumstances brief electrical stimuli or noradrenaline produced relaxation, cessation of action potentials, and hyperpolarization.

The Mechanism of Caffeine Contracture

(1) The tension and membrane potential during the caffeine contracture of frog sartorius muscle were recorded simultaneously. (2) The membrane potential did not alter at all, while the contracture tension developed. (3) The threseold of electric stimulus for contraction did not change during caffeine contracture, and the contraction by electric stimulus was superposed on the contracture. The nature of caffeine contracture, therefore, would be similar as a normal contraction. (4) In the hypertonic Ringer's solution, containing 2.5-3.0 times of NaCl, in which muscle can not contract by electric stimulus in spite of the appearance of action potential, caffeine could still, produce a contracture. (5) Caffeine could produce a contracture in the exausted muscle. (6) Caffeine may stimulate directly the second intermediate process (activation process) between action potential and contraction, and the hypertonicity may block the first one (spike-activation link).

Evoked Single Cortical Unit Activity in the Primary Cortical Receiving Areas

Amassian and Thomas are somewhat bold in implying that the complexities of the cortex can be reduced to no more than these simple and consistent patterns of response. Apart from their use of paralytic drugs, the main difference between our techniques lies in the size of electrodes used; mine were “of less than 5 µ diameter” and the action potentials of many millivolts amplitude were recorded only from electrodes of about 1 µ tip diameter. It is probable that electrodes of 4–12 µ tip diameter record distinct action potentials only from particularly large cells, which tend to be well separated, and this may be responsible for the simple and consistent responses obtained. Regarding the reproducibility of small electrode recordings, I have found that in a long series the number of action potentials evoked by a stimulus may vary widely; but there is a fairly constant latency at any one locus for the first appearance of action potentials belonging to a given group.