DOPAMINE CAUSES STIMULATION OF PROTEIN-KINASE-C IN RAT RENAL PROXIMALTUBULES BY ACTIVATING DOPAMINE D-1 RECEPTORS

Although it is suggested that in the renal proximal tubules, dopamine D-1 receptor activation causes inhibition of Na+/K(+)ATPase via a phos pholipase C and protein kinase C coupled pathway, the direct stimulati on of protein kinase C by dopamine has not been reported. The present study was designed to examine the effects of dopamine and selective do pamine D-1 receptor and dopamine D-2 receptor agonists on protein kina se C activity. The renal proximal tubule suspensions were obtained fro m male Sprague-Dawley rats. The tubules were incubated separately with dopamine and fenoldopam in the presence or absence of dopamine D-1 re ceptor antagonist, SCH 23390 yl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benza zepine]). The protein kinase C activity was measured by using a kinase target peptide, conjugated to a fluorescent molecule in water. The am ino acid sequence of this peptide is, Serine-Valine-Alanine-Alanine-Ly sine(PKSRTLSVAAK). We found that dopamine and fenoldopam dro-1-(4-hydr oxyphenyl)-1H-3-benzazepine-7,8-diol] produced concentration-dependent increases in protein kinase C activity, which was blocked by SCH 2339 0. However, the dopamine D-2 receptor agonist, bromocriptine yl)-5'-(2 -methylpropyl)ergo-taman-3',6',18-trione] failed to stimulate protein kinase C activity at all the concentrations tested. These results prov ide direct evidence that dopamine stimulates protein kinase C activity via activation of dopamine D-1 receptors.