Effects of ouabain and calcium on potassium balance of isolated guinea pig ventricle

¹ Departments of Pharmacology, University of Cincinnati College of Medicine, Cincinnati, Ohio, and Northwestern University Medical School, Chicago, Illinois

Isolated guinea pig ventricles were perfused as follows: A—45 min with normal Krebs-Ringer solution containing tracer amounts of K⁴² (NKR*); B—15 min with NKR*, 15 min with KR* in which half the calcium was replaced with sodium (Ca/2-KR*), 15 min with NKR*; C—15 min with NKR*, 15 min with Ca/2-KR*, 15 min with Ca/2-KR* + 10^–6 m ouabain; D—15 min with NKR*, 15 min with NKR* + 3.4 x 10^–4 m pentobarbital (PB), 15 min with NKR* + PB + ouabain. K influx, net K loss, contraction height, and flow rate were determined, and K efflux was calculated. Decreasing the external calcium concentration ([Ca]_e) decreased K efflux with no effect on K influx; restoring [Ca]_e increased K efflux without affecting influx. Ouabain decreased K influx more than it decreased K efflux. If [Ca]_e was constant, reducing the contraction height with PB did not affect K movements. These findings are consistent with the hypotheses that: 1) calcium and potassium can compete for fixed intracellular anionic binding sites and 2) calcium and ouabain produce their effects on K movements by different means.