Abstract
Our aim was to test the effect of hypotonicity and extracellular Ca^2+^ (Ca~o~) on cell volume and membrane potential (V~M~) in barnacle muscle cells. Under isotonic conditions the resting V~M~ of isolated cells mounted in the experimental chamber exposed to either Ca^2+^‐free or Ca^2+^‐containing (11 mM) solutions was − 46.3 ± 1.0mV (n = 24) and − 56.2 ± 0.9 mV (n = 38), respectively. In the absence of Ca~o~, the cells depolarized at a rate of 2.3 ± 0.47 mV/hr; the presence of Ca~o~ reduced this rate of depolarization by 2.9‐fold. Both in the absence or presence of Ca~o~, the cells swelled in response to hypotonicity but underwent regulatory volume decrease (RVD) when Ca~o~ was present. Addition of the Ca^2+^ channel blocker, verapamil (0.1 mM), inhibited the Ca~o~‐dependent RVD. The percentage of cells responding with RVD increased with larger hypotonic challenges. There was a Ca~o~‐independent direct relationship between cell swelling and membrane depolarization which can be explained by dilution of the concentration of intracellular K^+^ ([K^+^]~i~). RVD was accompanied by a small hyperpolarization (3.0 ± 0.38 mV/2 hr) which may represent increases in [K^+^]~i~ during cell shrinking and activation of a conductive pathway. The results indicate the following: (1) the presence of Ca~o~ stabilizes V~M~; (2) cell swelling produces a depolarization which can be explained by dilution of [K^+^]~i~; (3) cell swelling activates a verapamil‐sensitive Ca^2+^ influx responsible for promoting RVD; and (4) RVD is accompanied by a hyperpolarization which may result from activation of a conductive pathway. © 1994 Wiley‐Liss, Inc.