Protein kinase A activation is required for IL-1-induced nitric oxide production by cardiac myocytes

We have previously reported that interleukin-1 beta (IL-1) alone induced the transcription of inducible nitric oxide synthase (iNOS) mRNA and nitric oxide (NO) production by isolated neonatal rat cardiac myocytes (CM). The present studies were undertaken to explore the signal transduction pathways involved in IL-1-induced NO production by CN. The addition of IL-1 to CM resulted in a peak rise in both adenosine 3',5'-cyclic monophosphate (cAMP) and protein kinase A (PKA) activities by 10 min followed by rapid declines and return to basal levels within 60 min. The PKA inhibitor KIT-5720 completely blocked NO2- production by IL-1-stimulated CM (P < 0.01; n = 12). The protein kinase C (PKC) inhibitor, calphostin C, had no effect on NO2- production by IL-1-stimulated CM [P = not significant (NS); n = 12]. The addition of PKA + cAMP to cytosols derived from IL-1-treated CM did not directly enhance iNOS enzyme activity (P = NS; n = 3). CM treated with IL-1 alone stained positively for iNOS protein by immunohistochemistry. iNOS staining was absent in CM treated with IL-1 + KT-5720. KT-5720 resulted in an earlier disappearance of iNOS mRNA from IL-1-treated CM, as detected by semiquantitative reverse transcriptase-polymerase chain reaction. We report for the first time that PKA (but not PKC) activation is required for IL-1-induced NO production by CM.