Short-Term vs. Sustained Inhibition of Proximal Tubule Na, K-ATPase Activity by Dopamine: Cellular Mechanisms

Abstract

Dopamine (DA) produces a natriuresis attributed in part to inhibition of Na,K-ATPase activity (NKA) in the proximal tubule (PCT), and impairment in this inhibition has been linked to several forms of hypertension in animals. Here we examined whether the intracellular signaling mechanisms involved are the same in the early and late phases of this phenomenon. DA (1 microM) inhibited NKA similarly after 15 min (by 38%) or 180 min (by 36%) incubation, taken to represent short-term (ST) and sustained (Sd) pump regulation, respectively. Calphostin C, a specific inhibitor of protein kinase C (PKC), completely blocked the ST action of DA on NKA, whereas IP20, a specific inhibitor of protein kinase (PKA), had no effect. In contrast, IP20 completely abolished the Sd (180 min) inhibition by DA, whereas calphostin C had only a partial or variable effect. The DA-1 agonist fenoldopam (which does not activate PKC but increases cAMP) alone failed to inhibit the pump at 180 min (as it does also in the short-term in PCT), suggesting that ST inhibition is required for the Sd effect to occur. Furthermore, PTH1-34, a known ST inhibitor of NKA suppressed the pump at 180 min (by 46%), but unlike in the short-term, this effect was completely prevented by IP20. In contrast, PTH3-34, which does not stimulate adenylyl cyclase or activate PKA, caused only a small (19%) and variable Sd inhibition. In conclusion, short-term inhibition of the PCT pump by dopamine is mediated via PKC, whereas the sustained inhibition requires the PKA pathway in addition to the ongoing PKC-mediated effect.

Dopamine D 1 Receptor and Protein Kinase C Isoforms in Spontaneously Hypertensive Rats

“…7 Beyond 15 minutes, inhibition of PKC activity does not affect the ability of dopamine to inhibit Na ϩ ,K ϩ -ATPase activity in PT. 9 These data taken together suggest that D 1 -like receptors regulate PKC isoform expression differently from adrenergic and Ang II receptors. The differential regulation of PKC isoform expression by these receptors could account for their differential effect on sodium transport in normotensive animals.…”

“…14,15 In normotensive animals, dopamine, via D 1 -like receptors, decreases sodium transport in renal PT in part by the stimulation of PKC activity. 9,12,13 It is not readily apparent how an increase in PKC activity due to norepinephrine, Ang II, and dopamine can lead to an increase in sodium transport in one instance (norepinephrine and Ang II) and a decrease in another instance (dopamine). The differential effect on sodium transport may be due to differential effects on PKC isoforms; D 1 -like agonists (presumably acting on D 1 -like receptors) had no effect on PKC-␣ and PKC-but decreased PKC-␦ and PKC-expression, the opposite of the effect of norepinephrine and Ang II.…”

“…9,12,13 Moreover, a failure of dopamine and D 1 -like agonists to increase PKC activity has been reported to be a cause of the failure of these ligands to inhibit Na ϩ ,K ϩ -ATPase activity in renal PT in SHR. 13 We have found that D 1 -like agonists inhibit the expression of PKC-␦ and PKCin WKY but stimulate it in SHR at 10 and 60 minutes.…”

“…Thus, dopamine increases PKC activity and decreases Na ϩ ,K ϩ -ATPase in renal PT. 8,9,12,13 In contrast, norepinephrine and Ang II increase PKC, Na ϩ ,K ϩ -ATPase, 14,15 and Na ϩ /H ϩ exchanger activity. 15 The mechanism through which these receptors produce opposing effects in the kidney has not been studied but may relate to their differing regulation of PKC isoform expression and activity.…”

“…6 Dopamine decreases renal sodium transport by adenylyl cyclase/protein kinase A (PKA) and phospholipase C (PLC)/ PKC-dependent and -independent mechanisms. [7][8][9][10][11][12][13][14] However, other receptors (eg, angiotensin II [Ang II] and ␣-adrenergic receptors) also increase PKC activity but decrease sodium excretion.…”