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

1. Human isolated subcutaneous arteries were mounted in a myograph and isometric tension measured. In some experiments, intracellular calcium [Ca(2+)](i) was also measured using fura-2. 2. Angiotensin II (100 pM – 1 μM) increased [Ca(2+)](i) and tone in a concentration-dependent manner. The effects of angiotensin II (100 nM) were inhibited by an AT(1)-receptor antagonist, candesartan (100 pM). 3. Ryanodine (10 μM), had no effect on angiotensin II-induced responses, but removal of extracellular Ca(2+) abolished angiotensin II-induced rise in [Ca(2+)](i) and tone. Inhibition of Ca(2+) entry by Ni(2+) (2 mM), also inhibited angiotensin II responses. The dihydropyridine, L-type calcium channel antagonist, amlodipine (10 μM), only partially attenuated angiotensin II responses. 4. Inhibition of protein kinase C (PKC) by chelerythrine (1 μM), or by overnight exposure to a phorbol ester (PDBu; 500 nM) had no effect on angiotensin II-induced contraction. 5. Genistein (10 μM), a tyrosine kinase inhibitor, inhibited angiotensin II-induced contraction, but did not inhibit the rise in [Ca(2+)](i), suggesting that at this concentration it affected the calcium sensitivity of the contractile apparatus. Genistein did not affect responses to norepinephrine (NE) or high potassium (KPSS). 6. A selective MEK inhibitor, PD98059 (30 μM), inhibited both the angiotensin II-induced contraction and rise in [Ca(2+)](i), but had no effect on responses to NE or KPSS. 7. AT(1) activation causes Ca(2+) influx via L-type calcium channels and a dihydropyridine-insensitive route, but does not release Ca(2+) from intracellular 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 contraction in human subcutaneous resistance arteries

The Gβ1 and Gβ3 subunits differentially regulate rat vascular Kv7 channels

Within the vasculature Kv7 channels are key regulators of basal tone and contribute to a variety of receptor mediated vasorelaxants. The Kv7.4 isoform, abundant within the vasculature, is key to these processes and was recently shown to have an obligatory requirement of G-protein βγ subunits for its voltage dependent activity. There is an increasing appreciation that with 5 Gβ subunits and 12 Gγ subunits described in mammalian cells that different Gβxγx combinations can confer selectivity in Gβγ effector stimulation. Therefore, we aimed to characterize the Gβ subunit(s) which basally regulate Kv7.4 channels and native vascular Kv7 channels. In Chinese Hamster Ovary cells overexpressing Kv7.4 and different Gβx subunits only Gβ1, Gβ3, and Gβ5 enhanced Kv7.4 currents, increasing the activation kinetics and negatively shifting the voltage dependence of activation. In isolated rat renal artery myocytes, proximity ligation assay detected an interaction of Kv7.4 with Gβ1 and Gβ3 subunits, but not other isoforms. Morpholino directed knockdown of Gβ1 in rat renal arteries did not alter Kv7 dependent currents but reduced Kv7.4 protein expression. Knockdown of Gβ3 in rat renal arteries resulted in decreased basal K+ currents which were not sensitive to pharmacological inhibition of Kv7 channels. These studies implicate the Gβ1 subunit in the synthesis or stability of Kv7.4 proteins, whilst revealing that the Gβ3 isoform is responsible for the basal activity of Kv7 channels in native rat renal myocytes. These findings demonstrate that different Gβ subunits have important individual roles in ion channel regulation