Glibenclamide-sensitive mechanism is involved in helodermin-produced vasodilatation in rat mesenteric artery.

Helodermin-caused vascular relaxation was simultaneously measured with intracellular Ca2+ concentration ([Ca2+]i) in rat mesenteric artery. Helodermin caused concentration-dependent relaxation in the mesenteric artery preconstricted with norepinephrine (NE). Helodermin-caused relaxation was accompanied by decrease in [Ca2+]i, D-cis-Diltiazem, a Ca2+ channel blocker, also lowered the [Ca2+]i and tension increased by NE. However, helodermin relaxed the artery more efficiently than D-cis-diltiazem, suggesting that the peptide decreased myofilament Ca2+ sensitivity. The vascular relaxation and the corresponding decrease in [Ca2+]i induced by helodermin were partly, but significantly attenuated by glibenclamide. Helodermin-induced vascular responses were mimicked by vasoactive intestinal polypeptide (VIP) or forskolin. Furthermore, helodermin increased cAMP contents in the mesenteric artery. These findings show that vasodilatation induced by helodermin is attributable to lowered [Ca2+]i of arterial smooth muscle partly through the activation of glibenclamide-sensitive K+ channels, and to decrease in the myofilament Ca2+ sensitivity. The increase in the cellular cAMP content probably plays a key role in the peptide-induced vasorelaxation.

Potentiation by endothelin-1 of Ca2+ sensitivity of contractile elements depends on Ca2+ influx through L-type Ca2+ channels in the canine cerebral artery.

1. Endothelin-1 (ET-1) contracted canine cerebral artery in a concentration-dependent manner with an increase in intracellular Ca2+ concentration ([Ca2+]i), and at higher concentrations it produced a greater contraction with a smaller increase in [Ca2+]i. 2. Ca2+ channel antagonist such as d-cis-diltiazem inhibited the tension more effectively than the [Ca2+]i increased by ET-1. 3. In Ca(2+)-free solution containing 0.2 mM EGTA, ET-1 elicited a transient increase in [Ca2+]i and tension. 4. In the Staphylococcus aureus alpha-toxin-permeabilized artery, ET-1 shifted the pCa-tension relationship leftwards in the presence of GTP. 5. These findings suggest that ET-1 contracts the canine cerebral artery by increasing not only the Ca2+ influx through L-type Ca2+ channels, but also Ca2+ release from the intracellular storage sites, and also Ca2+ sensitivity of contractile elements. The degree of Ca2+ sensitivity is strongly affected by [Ca2+]i which is increased by the Ca2+ influx through L-type Ca2+ channels.

Ca2+ handling mechanisms underlying neuropeptide Y-induced contraction in canine basilar artery.

The effects of neuropeptide Y on isometric tension simultaneously measured with cytosolic Ca2+ concentration ([Ca2+]cyt) and Ca2+ sensitivity of contractile elements were studied in isolated canine basilar arteries. Neuropeptide Y (1-100 nM) increased [Ca2+]cyt and tension in a concentration-dependent and parallel manner, whereas 9,11-dideoxy-11 alpha,9 alpha-epoxymethano prostaglandin F2 alpha (U46619) (10-100 nM), a thromboxane A2 mimetic, produced a large contraction with a small increase in [Ca2+]cyt. Ca2+ channel antagonists such as d-cis-diltiazem (10 mM) abolished both [Ca2+]cyt and tension augmented by neuropeptide Y. In Ca(2+)-free solution containing 0.2 mM EGTA, neuropeptide Y did not change [Ca2+]cyt and tension, whereas U46619 transiently increased both of them. Furthermore, neuropeptide Y apparently did not affect the Ca2+ sensitivity when assessed in the artery permeabilized with Staphylococcus aureus alpha-toxin, whereas U46619 augmented it. These findings suggest that neuropeptide Y-induced contraction in the canine basilar artery is produced mainly by Ca2+ influx through L-type Ca2+ channels.

Quick stretch increases the production of inositol 1,4,5-trisphosphate (IP3) in porcine coronary artery.

The present study was undertaken to know whether the formation of inositol 1,4,5-trisphosphate (IP3) is increased by quick stretch, a dynamic mechanical stimulus in porcine coronary artery in order to inquiry the possibility that IP3 could mediate Ca2+ release in the stretch-induced contraction. Quick stretching of a helical strip of porcine coronary artery at a rate of 10 cm/sec, the amount of stretch equivalent to 140% of the initial muscle length (= 100%), and the stimulus period of 30 sec with 20-min intervals, produced delayed contraction. Quick stretching increased the content of IP3 about three-fold over the control basal level, which always preceded the contraction. A putative phospholipase C inhibitor, 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (NCDC), abolished the increase in the formation of IP3 and partially inhibited the stretch-induced contraction. The results suggest that quick stretching increases the formation of IP3 through a possible mechanism for activation of phospholipase C, which may lead to release of Ca2+ into myoplasm and to further activation of the contractile elements.

Stretching releases Ca2+ from intracellular storage sites in canine cerebral arteries.

Mechanical stretch applied to canine cerebral artery produced myogenic contraction. The contraction of the artery in response to quick stretch was dependent on not only the transmembrane influx of Ca2+ through 1,4-dihydropyridine-sensitive Ca2+ channels but also the release of Ca2+ from intracellular storage sites: the stretch-produced contractile component that was resistant to 0.1 microM nicardipine, a Ca(2+)-channel antagonist, was inhibited by about 50% after treatment with ryanodine, and was almost completely suppressed by 0.1 mM 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate, a putative phospholipase C inhibitor, or by lowering the temperature from 35 to 20 degrees C. The results suggest that in addition to transmembrane influx of Ca2+ through L-type Ca2+ channels, the release of Ca2+ from both ryanodine-sensitive and -insensitive intracellular storage sites, which increases intracellular Ca2+, accounts for the stretch-induced contraction of canine basilar artery. It seems also possible that inositol 1,4,5-trisphosphate is a common mediator for the release of Ca2+ from both types of intracellular storage sites.