European Journal of Pharmacology, 250 (1993) 431-437 © 1993 Elsevier Science Publishers B.V. All rights reserved 0014-2999/93/$06.00 EJP 53442 Effects of isoquinoline derivatives, HA1077 and H-7, on cytosolic Ca 2+ level and contraction in vascular smooth muscle Satoko Takizawa *, Masatoshi Hori, Hiroshi Ozaki and Hideaki Karaki Department of Veterinary Pharmacology, Faculty of Agriculture, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan Received 29 April 1993, revised MS received 5 October 1993, accepted 8 October 1993 The effects of isoquinoline derivatives, HA1077 (1-[5-isoquinolinesulfonyl]-homopiperazine) and H-7 (1-[5-isoquinoline- sulfonyl]-2-methylpiperazine), on cytosolic Ca 2÷ levels ([Ca2+]i) and muscle tension were examined in vascular smooth muscle of rat aorta. High K ÷ (72.7 mM) and norepinephrine (1/zM) induced a sustained contraction with a sustained increase in [Ca2+]i . HA1077 and H-7 (3-10/xM) inhibited the increase in muscle tension more strongly than the increase in [Ca2+] i. Verapamil (10 /xM) completely inhibited the increase in [Ca2+] i and the contraction induced by high K ÷ whereas it inhibited the increase in [Ca2+]i more strongly than the contraction due to norepinephrine. The verapamil-insensitive portion of the norepinephrine-in- duced contraction was inhibited by HA1077 or H-7. In Ca2+-free solution, 0.1 /xM norepinephrine induced a transient increase in [Ca2+] i and muscle tension. The transient contraction was inhibited by 10/xM HA1077 or 10/zM H-7 without inhibiting the increase in [Ca2+]i . 12-Deoxyphorbol 13-isobutyrate (DPB) (1 /xM) caused a sustained contraction, and this contraction was inhibited by HA1077 and H-7 at similar concentrations needed to inhibit the contractions induced by high K + or nor- epinephrine. In rabbit mesenteric artery permeabilized with Staphylococcus aureus a-toxin, 100/zM HA1077 and 100 /zM H-7 inhibited the contraction induced by 0.3/zM Ca 2+. These results suggest that the inhibitory effects of isoquinoline derivatives, HA1077 and H-7, are due to a decrease in [Ca2+] i and in the Ca 2+ sensitivity of contractile elements in vascular smooth muscle. HA1077; H-7; Ca 2+ level, cytosolic; Relaxation; Aorta, rat; Smooth muscle, vascular I. Introduction An isoquinoline sulfonamide, H-7 (1-[5-isoquino- linesulfonyl]-2-methylpiperazine), has been suggested to be a relatively selective inhibitor of protein kinase C, and this compound has been widely used in experi- ments with biological systems (see Hidaka and Hagi- wara, 1987). However, Garland et al. (1987) suggested that H-7 is competitive at the ATP binding site, but not at the diacylglycerol binding site, of the kinases and therefore may not show any selectivity for protein kinase C. Ratz (1990) reported that H-7 nonselectively inhibits the contractions of rabbit femoral and renal arteries stimulated by high K + or phenylephrine. Recently, HA1077 (1-[5-isoquinolinesulfonyl]-homo- piperazine) was synthesized by modifying the structure of H-7. This compound inhibits cerebral vasospasm * Corresponding author. Tel. +81-3-3812-2111 Ext. 5395, fax+81-3- 5802-2959. without having much effect on blood pressure (Takayasu et al., 1986). Asano et al. (1987, 1989) re- ported that HA1077 inhibits the contractions of rabbit aorta induced by high K + and receptor agonists, such as norepinephrine, histamine and angiotensin II, and also inhibits the activity of various protein kinases. It was also found that HA1077 inhibits myosin light chain phosphorylation in vascular smooth muscle stimulated by high K + and prostaglandin F2~ (Seto et al., 1991). However, the effects of HA1077 on cytosolic Ca 2+ level ([Ca2+] i) have not been examined yet. In order to clarify further the mechanism of the relaxing action of the isoquinoline derivatives in vascu- lar smooth muscle, we examined the effects of H-7 and HA1077 on [Ca2+]i and muscle tension using the fura-2 method in isolated rat aorta. We also studied the effects of these compounds on muscle permeabilized with staphylococcal a-toxin. The results of the experi- ments suggest that HA1077 and H-7 inhibit vascular smooth muscle contraction by inhibiting the increase in [Ca2+]i and also by decreasing the Ca 2+ sensitivity of contractile elements.