AJP - Cell Physiology, Vol 248, Issue 3 330-C336, Copyright © 1985 by American Physiological Society
Effect of insulin on intracellular pH in frog skeletal muscle fibers
R. W. Putnam
The effect of insulin on intracellular pH (pHi) and membrane potential was
studied in frog semitendinosus muscle fibers, using recessed-tip
pH-sensitive glass microelectrodes and conventional 3 M KCl-filled
microelectrodes. After a lag period of approximately 20 min, insulin [1
mU/ml, 0.1% bovine serum albumin (BSA)] produced a slow hyperpolarization
of 2-5 mV and an alkalinization of 0.05-0.10 pH unit, which were both
completed within 1 h and were not reversed by washing in insulin-free
solution for 1 h. The effect of insulin on the pHi recovery rate from
CO2-induced acidification was examined at various membrane voltages. At
normal membrane voltage, insulin (400 mU/ml, no BSA) slightly increased the
slow pHi recovery (from 0.01 to 0.04 delta pH/h). In fibers depolarized in
15 mM K to about -50 mV, insulin nearly tripled the recovery rate (from
0.05 to 0.13 delta pH/h). This insulin-induced recovery was abolished by 1
mM amiloride, a Na-H exchange inhibitor. The increased pHi recovery in 15
mM K thus represents an increased Na-H exchange, which may be due to an
interaction between insulin and either membrane depolarization, per se, or
increased intracellular Ca. In fibers depolarized in 50 mM K to about -25
mV, insulin did not affect recovery (0.28 delta pH/h). This lack of insulin
effect might be due to fiber swelling or to the difference in the time
course of elevation of intracellular Ca at -25 and -50 mV. These results
are consistent with an alkalinizing effect of insulin in frog muscle
mediated by Na-H exchange.
