Inhibition of in vitro renin release by low extracellular K

Renin release from rat renal cortical slices was measured as a function of the concentration of K in the incubation medium. Release was completely abolished within a 30-minute period of exposure to nominally K-free or to 1.0 mM K media. Release tended to increase with increasing K, over the range 2 – 6 mM, although release was near maximal at 2.0 mM K. Omission of Ca from the incubation medium prevented the full inhibitory effect of nominally K-free medium. It is suggested that Ca accumulation, perhaps via Na-Ca exchange, is required to produce the inhibitory effect of low K medium on renin release in vitro.