Activators of protein kinase C inhibit sodium transport in A6 epithelia

Abstract

To evaluate the role of protein kinase C in sodium transport via amiloride-sensitive sodium channels, we studied the effect of activators of protein kinase C on short-circuit current in epithelia formed by A6 cells in culture. In A6 epithelia, short-circuit current is equivalent to net sodium transport and is blocked by low concentrations of amiloride added to the solution bathing the apical surface. After any of four different activators of protein kinase C [phorbol 12,13-dibutyrate (20 ng/ml), phorbol 12-myristate 13-acetate (20 ng/ml), 1-oleoyl-2-acetylglycerol (50 micrograms/ml), and mezerein (10 ng/ml)] was added to the solution bathing the apical surface, short-circuit current fell, and electrical resistance rose. Nystatin added to the apical solution reversed the inhibition of short-circuit current, indicating that activators of protein kinase C inhibited transport at amiloride-sensitive sodium channels in the apical plasma membrane. Under some conditions, the activators also stimulated amiloride-insensitive short-circuit current. The ion transport represented by the amiloride-insensitive short-circuit current appears to be the result of basal to apical transport of chloride, but this has not been established conclusively.

Phorbol 12-myristate 13-acetate down-regulates Na,K-ATPase independent of its protein kinase C site: decrease in basolateral cell surface area.

“…The lack of effect of amiloride on the PMA-induced ISC indicated that this current was not via the amiloride-sensitive sodium channel and that, furthermore, PMA inhibited the preexisting amiloride-sensitive sodium transport. These observations correspond to those made by Yanase and Handler (1986) who concluded that activators of PKC inhibit sodium transport and stimulate an amiloride-resistant ISC' which most likely represents basolateral to apical chloride transport.…”

“…Several studies have shown that direct PKC stimulation and hormones acting via PKC stimulation decrease the activity of the amiloride-sensitive epithelial sodium channel and hence sodium reabsorption in the cortical collecting duct and A6 epithelia (Yanase and Handler, 1986;Hays et al, 1987;Ling and Eaton, 1989;Ling et al, 1992;Takeda et al, 1994;Frindt et al, 1996). In the present study, we confirm that PKC stimulation by PMA blocks the amiloride-sensitive short circuit current in A6 epithelia while it stimulates an amiloride-resistant ISc, which most likely corresponds to Cl secretion ( Figure 1; Yanase and Handler, 1986).…”

“…A similar role for PKC in sodium channel regulation by sodium feedback and prostaglandin E2 has been described in X. laevis A6 cells that are used as a model for cortical collecting duct principal cells (Ling and Eaton, 1989;Eaton et al, 1995). A direct stimulation of PKC by phorbol esters has also been shown to inhibit amiloride-sensitive sodium transport and to activate Cl conductive pathways leading to Cl secretion across A6 epithelia (Yanase and Handler, 1986).…”

Axial heterogeneity of vasopressin-receptor subtypes along the human and mouse collecting duct

“…A PKC-dependent AQP2 retrieval from apical membrane of principal cells has also been observed (56). Other studies suggest that calcium/PKC-coupled signaling not only inhibits water flow but also inhibits Na ϩ absorption and K ϩ secretion in the collecting ducts (26,46,59).…”

Protein Kinase C Isoform Antagonism Controls BNaC2 (ASIC1) Function

“…The effects of PKC on amiloride-sensitive Na ϩ transporting pathways were even more complex and diverse. Activation of PKC greatly diminished Na ϩ transport in A6 cells (52,53) and in the LLC-PK1 epithelial cell line (54). PKC also attenuated the activity of purified renal amiloride-sensitive sodium channels (55).…”