Changes in passive electrical properties of guinea-pig ventricular muscle exposed to low K+ and high Ca2+ conditions

Changes in passive electrical properties of guinea-pig papillary muscle exposed to low K+, high Ca2+ conditions were examined using a single sucrose gap technique. While quiescent preparations exposed for 5 mins did not develop delayed afterdepolarizations, those placed in the test solution for 30 mins with or without stimulation developed afterdepolarizations. Changes occurring during a short exposure to low K+, high Ca2+ solution were increases in membrane resistance, membrane time constant and space constant by 47%, 83% and 17% compared with the control, respectively. There were no significant changes in internal longitudinal resistance and membrane capacity. During long exposure to the test solution (30 mins), delayed afterdepolarizations developed. There were similar increases in membrane resistance and in time constant as found during the short exposures. Internal longitudinal resistance was calculated to have increased by 24% during the long exposure. A 19% increase in membrane capacity was also found during the test condition. High Ca2+ or low K+ alone did not cause a significant increase in internal longitudinal resistance. The conduction velocity in the longitudinal direction decreased from 107 +/- 23 cm/s during the control to 80 +/- 7 cm/s during the test period for 30 mins. These results suggest that, in addition to the abnormal impulse formation based on afterdepolarizations, low K+, high Ca2+ solution changes the passive electrical properties of the fibers, resulting in a lower rate of impulse conduction.