Abstract
Fibroblastic L cells show spontaneous oscillation (about 4 cycle/min) of membrane potential between -15mV and -40mV under the normal condition, and respond with single hyperpolarizing responses to electrical or mechanical stimuli. In addition, several serum proteins (ex. β-lipoprotein) applied to the membrane induce sustained hyperpolarizing responses.
Ionic mechanism of such hyperpolarizing responses is deduced from a variety of elec- trophysiological studies. Mechanical, electrical or chemical stimuli applied to the membrane of L cells elicit Ca2+ influx across the cell membrane. An increase in the intracellular Ca2+ concentration thus induced triggers an openg of so-called Ca2+ -activated K+ channel, and then the K+ conductance increase thus developed produces a hyperpolarizing response. Oscillation would be induced by the periodic changes in the intracellular Ca2+ concentration, which could be brought about by a feed-back relationship between a carrier-mediated Ca2+ entry and an active Ca2+ extruding pump on the plasma membrane.
Possible physiological role of a hyperpolarizing response in fibroblasts was also discussed in the light of its ionic mechanism.
