Mechanism of action of angiotensin II in human isolated subcutaneous resistance arteries

1 Human isolated subcutaneous arteries were mounted in a myograph and isome tric tension measured. In some experiments, intracellular calcium [Ca2+](i) was also measured using fura-2. 2 Angiotensin II (100 pM - 1 muM) increased [Ca2+](i) and tone in a concent ration-dependent manner. The effects of angiotensin II (100 nM) were inhibi ted by an AT(1)-receptor antagonist, candesartan (100 pM). 3 Ryanodine (10 muM), had no effect on angiotensin II-induced responses, bu t removal of extracellular Ca2+ abolished angiotensin II-induced rise in [C a2+](i) and tone. Inhibition of Ca2+ entry by Ni2+ (2 mm), also inhibited a ngiotensin II responses. The dihydropyridine, L-type calcium channel antago nist, amlodipine (10 pm), only partially attenuated angiotensin II response s. 4 Inhibition of protein kinase C (PKC) by chelerythrine (1 muM), or by over night exposure to a phorbol ester (PDBu; 500 nm) had no effect on angiotens in II-induced contraction. 5 Genistein (10 muM), a tyrosine kinase inhibitor, inhibited angiotensin II -induced contraction, but did not inhibit the rise in [Ca2+](i), suggesting that at this concentration it affected the calcium sensitivity of the cont ractile apparatus. Genistein did not affect responses to norepinephrine (NE ) or high potassium (KPSS). 6 A selective MEK inhibitor, PD98059 (30 muM), inhibited both the angiotens in II-induced contraction and rise in [Ca2+](i), but had no effect on respo nses to NE or KPSS. 7 AT(1) activation causes Ca2+ influx via L-type calcium channels and a dih ydropyridine-insensitive route, but does not release Ca2+ from intracellula r sites. Activation of tyrosine kinase(s) and the ERK 1/2 pathway, but not classical or novel PKC, also play a role in angiotensin II-induced contract ion in human subcutaneous resistance arteries.