Abstract
Studies from our laboratory have demonstrated rapid (<1 min) non-genomic activation of Na+-H+ exchange and potassium recycling by mineralocorticoids in human and rat colonic epithelium. It has previously been demonstrated that Na+-H+ exchange may be stimulated by protein kinase C (PKC) activation; therefore, we examined the effect of mineralocorticoids on PKC activity in rat colonic epithelium. Activation (after 15 min of incubation) of basal PKC activity was observed in cytosolic fractions of rat colonic epithelium by aldosterone, fludrocortisone, and deoxycorticosterone acetate. In all instances, PKC activation was inhibited by the PKC inhibitor bisindolylmaleimide (GF109203X). Hydrocortisone failed to activate PKC activity. Stimulation of basal intracellular free calcium [Ca2+]i was observed, in isolated rat colonic crypts, following aldosterone addition. This stimulatory effect was inhibited by the PKC inhibitor, chelerythrine chloride. Hydrocortisone failed to increase [Ca2+]i. These results indicate that intracellular signaling for aldosterone involves changes in [Ca2+]i via activation of PKC. Since the stimulation of PKC and increase in [Ca2+]i are apparent at normal circulating levels of aldosterone, our findings have major implications for the reassessment of mineralocorticoid effects on electrolyte homeostasis.
Highlights
Aldosterone has been reported to produce a rapid in vitro effect on intracellular electrolyte concentrations and cell volume and activity of the Naϩ-Hϩ exchanger in human mononuclear leukocytes [1,2,3,4]
In fractionated samples of rat colonic epithelium, approximately 75% of protein kinase C (PKC) activity is associated with the cytosolic fraction and the remainder localized to the membrane fraction
Basal PKC activity was significantly stimulated, following a 15-min incubation, in the presence of aldosterone (0.01–100 nM; p Ͻ 0.005), fludrocortisone (0.01–100 nM; p Ͻ 0.005), and deoxycorticosterone acetate (DOCA) (0.01–100 nM; p Ͻ 0.01) in cytosolic fractions isolated from rat colonic epithelium
Summary
Aldosterone has been reported to produce a rapid in vitro effect (acute onset within 1–2 min) on intracellular electrolyte concentrations and cell volume and activity of the Naϩ-Hϩ exchanger in human mononuclear leukocytes [1,2,3,4]. Rapid effects of aldosterone on free intracellular calcium [Ca2ϩ]i in vascular smooth muscle and endothelial cells have recently been demonstrated [6]. These fast responses to aldosterone are incompatible with the involvement of the classical steroid hormone pathway. It has been shown that Naϩ-Hϩ exchange may be stimulated by protein kinase C (PKC) activation [12] Many extracellular signals such as hormones, neurotransmitters, growth factors and other biologically active substances induce both Ca2ϩ mobilization and phosphoinositide turnover in their target cells [13]. The aims of this study were to investigate the effect of mineralocorticoids on PKC activity in rat distal colonic epithelium and the effects of aldosterone on [Ca2ϩ]i in rat colonic crypts
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
