The structure of helokinestatin-5 and its biosynthetic precursor from Gila monster (Heloderma suspectum) venom: Evidence for helokinestatin antagonism of bradykinin-induced relaxation of rat tail artery smooth muscle

Whole cell patch-clamp recordings were carried out on smooth muscle cells from rat tail artery in short-term culture to verify the existence of and to characterize the calcium channels that are present. Two types of voltage-dependent calcium channels were identified in 55 of 63 cells studied. The T-type calcium channel was activated at -50 mV, and the peak inward current occurred at -10 mV, whereas the L-type channel was activated at -20 mV, and the peak inward current occurred at +10 or +20 mV. The T-type channel current inactivated quickly in contrast to the much slower inactivation of the L-channel current. The voltage dependence of steady-state inactivation of the two channels was similar to that reported for other vascular smooth muscle preparations. An internal solution containing Cs2-aspartate maintained the calcium-channel currents for at least 20 min with only a 5-10% decline. BAY K 8644 had no effect on T-channel currents, but the L-channel current was increased by at least a factor of two. In addition, BAY K 8644 shifted the activation threshold, the peak inward current, and the steady-state inactivation-activation curves of L-type channel currents in the direction of hyperpolarization.

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Calcium channel activation in vascular smooth muscle by BAY K 8644

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y84-233 ◽

1984 ◽

Vol 62 (11) ◽

pp. 1401-1410 ◽

Cited By ~ 85

Author(s):

C. M. Su ◽

V. C. Swamy ◽

D. J. Triggle

Keyword(s):

Smooth Muscle ◽

Dose Response ◽

Response Curve ◽

Bay K 8644 ◽

Rat Tail Artery ◽

Channel Activation ◽

Tail Artery ◽

Voltage Dependent ◽

Adrenoceptor Agonists ◽

Rat Tail

BAY K 8644 (methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)pyridine-5-carboxylate) and CGP 28 392 (ethyl-4(2-difluoromethoxyphenyl)-1,4,5,7-tetrahydro-2-methyl-5-oxofuro-[3,4-b]pyridine-3-carboxylate) are closely related in structure to nifedipine and other 1,4-dihydropyridine Ca2+ channel antagonists. However, both BAY K 8644 and CGP 28 392 serve as activators of Ca2+ channels. In the rat tail artery, responses to BAY K 8644 are dependent upon [Formula: see text] and prior stimulation by K+ or by the α-adrenoceptor agonists, phenylephrine and BHT 920 (6-allyl-2-amino-5,6,7,8,-tetrahydro-4H-thiazolo[4,5-d]azepin dihydrochloride). Responses are blocked noncompetitively by the Ca2+ channel antagonists D-600 ((−)-D-600 > (+)-D-600) and diltiazem, but competitively by nifedipine (pA2 = 8.27). This suggests that activator and inhibitor 1,4-dihydropyridines interact at the same site. BAY K 8644 potentiates K+ responses and Ca2+ responses in K+-depolarizing media. The leftward shift of the K+ dose–response curve produced by BAY K 8644 suggests that this ligand facilitates the voltage-dependent activation of the Ca2+ channel. The pA2 value for nifedipine antagonism of BAY K 8644 responses is significantly lower than that for nifedipine antagonism of Ca2+ responses in K+ (25–80 mM) depolarizing media (9.4–9.6), suggesting that the state of the channel may differ according to the activating stimulus.

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