KCI‐Stimulated Renin Release

Abstract

Renin released from rat renal cortical slices was measured under conditions designed to elevate intracellular Ca2+. Rats were sacrificed by cervical dislocation and the kidneys flushed retrograde with 0.9% saline. The kidneys were then removed, slices (-1 mm thick, 10-30 mg) prepared, placed in sealed 1-ml wells and superfused (250 pl/minute/well) using two bottles of Krebs-Ringers phosphate (KRP) buffer containing 5.9 mM KCI. One bottle was gassed with 0 2 / C 0 2 (19 : l), the other served as the vehicle for test agents. After one hour of superfusion, three consecutive superfusion periods of 30 minutes each (CI, CII, CIII) commenced, the superfusates collected on ice and assayed for renin activity.' Norepinephrine-depleted slices were prepared by dosing rats with 6-hydroxydopamine (6-HD), 100 mg/kg i.p. seven and four days before slice preparation (6-HD slices). Renin release rates were calculated as ng AI/ml superfusate/ 1-hour incubation, normalized to ng AI/hour/mg cortex/30minute superfusion and expressed as percent changes in release relative to CI. Antagonists superfused were verapamil, trifiuoperazine, indomethacin, and timolol. All were dissolved in KRP and superfused in accordance with TABLE 1.Supraphysiological KCl concentrations have been demonstrated to inhibit renin release by enhancing Ca2+ influx through voltage-dependent channels." As predicted from the results of earlier experiments,24 when the KCl concentration of the KRP was increased from 5.9 mM to 60 mM at the start of CII and continued to the end of CIII, an inhibition of renin release occurred (TABLE 1). However, the inhibitory response occurred late (CIII) and, was, in fact, preceded by a stimulatory response (CII). This biphasic response was specifically associated with elevated KCl concentration as slices superfused with 5.9 mM KCI-KRP exhibited only minor changes in release (TABLE 1). Hence, the superfusion technique unmasked a stimulatory response to a supraphysiological concentration of KCl. This effect has been undetected when, using supraphysiological KCl, renal cortical slices were maintained in a static bathing medium.24KCl-evoked release in CII was antagonized (TABLE 1) by blocking Ca2+ influx through voltage-dependent channels (verapamilO.05-5 pM), inhibiting Ca'+-calmodulin association (trifluoperazine), inhibiting prostaglandin synthesis (indomethacin), and 8-adrenergic antagonism (timolol). 6-HD slices also failed to release renin when superfused with 60 mM KCl-KRP (FIG. 1). Accordingly, the stimulatory response in aAddress correspondence to: