Recent findings implicate protein kinase C in regulation of contraction of uterine muscle (myometrium). However, the role of protein kinase C isoforms in myometrial contraction remains uncertain. Therefore, this study examined protein kinase Calpha's role in regulation of contraction and intracellular calcium concentration ([Ca2+](I)) of myometrium from term pregnant women. The authors demonstrated that protein kinase Calpha inhibitor Go6976 decreased the amplitude of potassium chloride-induced myometrial contractions in a time-dependent manner. The treatment of the myometrial strips with protein kinase Calpha-specific antisense oligodeoxynucleotides decreased the potassium chloride-induced contraction and [Ca2+](I) response to 39.3% + 6.8% and 50.0% + 3.3%, respectively, compared to control. The sense oligonucleotides treatment did not significantly change the potassium chloride responses (89.8% + 6.8% and 93.9% + 4.5% of the control for the contraction and [Ca2+](I), respectively). These data, coupled with the observation that protein kinase Calpha levels are elevated in the pregnant myometrium, suggest the involvement of protein kinase Calpha in regulation of human uterine contraction.