The Role of L- and T-Type Calcium Channels in Local and Remote Calcium Responses in Rat Mesenteric Terminal Arterioles

Abstract

Background/Aims: The roles of intercellular communication and T-type versus L-type voltage-dependent Ca²⁺ channels (VDCCs) in conducted vasoconstriction to local KCl-induced depolarization were investigated in mesenteric arterioles. Methods: Ratiometric Ca²⁺ imaging (R) using Fura-PE3 with micro-ejection of depolarizing KCl solution and VDCC blockers, and immunohistochemical and RT-PCR techniques were applied to isolated rat mesenteric terminal arterioles (n = 71 from 47 rats; intraluminal diameter: 24 ± 1 μm; length: 550–700 μm). Results: Local application of KCl (at 0 μm) led to local (ΔR = 0.54) and remote (ΔR = 0.17 at 500 μm) increases in intracellular Ca²⁺. Remote Ca²⁺ responses were inhibited by the gap junction uncouplers carbenoxolone and palmitoleic acid. Ca_V1.2, Ca_V3.1 and Ca_V3.2 channels were immunolocalized in vascular smooth muscle cells and Ca_V3.2 in adjacent endothelial cells. Local and remote Ca²⁺ responses were inhibited by bath application of L- and T-type blockers [nifedipine, NNC 55-0396 and R(–)-efonidipine]. Remote Ca²⁺ responses (500 μm) were not affected by abolishing Ca²⁺ entry at an intermediate position on the arterioles (at 200–300 μm) using micro-application of VDCC blockers. Conclusion: Both L- and T-type channels mediate Ca²⁺ entry during conducted vasoconstriction to local KCl in mesenteric arterioles. However, these channels do not participate in the conduction process per se.

The Vascular Conducted Response in Cerebral Blood Flow Regulation

“…This topic is still not completely resolved, but recent studies did not find a role for TTX-sensitive 13,25,29 or TTX-insensitive Na þ channels 18 in conducted depolarization in rat renal or mesenteric arterioles.…”

“…11,13,[27][28][29] For simultaneous recording of Ca 2 þ signals at multiple sites along an arteriole during a VCR, an objective with low magnification ( Â 20) and high numerical aperture and a sensitive CCD camera for capturing a sufficient amount of fluorescence has been used. 13,18 Conducted vasoconstriction is associated with an increase in [Ca 2 þ ] i in both the VSMC and the EC, and the change in [Ca 2 þ ] i showed an attenuation with distance from the local stimulation site that paralleled the degree of vasoconstriction. 13,18,27,29 The wide-field recordings of [Ca 2 þ ] i can be used as a measure of the conducted signal, and therefore provides detailed information on the strength of the conducted signal along the vessel.…”

Functional Importance of L- and P/Q-Type Voltage-Gated Calcium Channels in Human Renal Vasculature

“…Ca v s of the Ca v 3.2 and Ca v 3.1 types have been reported previously in endothelial cells in rats, 22,23 albeit with unclear function. The antibody specific for the T-type subunit Ca v 3.2 did not apply to human tissue, and we did not observe a Ca v 3.1 labeling of human renal endothelial cells.…”

T-type Ca2+channels and autoregulation of local blood flow

“…40,46,48,50,113 In small mesenteric arteries from wild-type mice nifedipine (1 mM) abolished myogenic tone at higher pressures, whereas there was no effect on tone at 40 mmHg. In agematched mice deficient in the Ca V 3.1 T-type channels, myogenic tone was abolished at lower pressures (40-80 mmHg), but at pressures above 80 mmHg the spontaneous myogenic tone was abolished by 1 mM nifedipine.…”

“…44,45 Moreover, in resistance vessels Ca V 3.1 and Ca V 3.2 T-type channel protein expression has been demonstrated by immunolocalization to VSMCs 46-51 as well as ECs. 48,49,51,52 Interestingly, in human cerebral arteries the T-type isoforms expressed are the Ca V 3.2 and Ca V 3.3 channels, with no expression of Ca V 3.1 channels. 53 Application of 15 mmHg extracellular pressure to SW620 human cancer cells causes mechanical activation of Ca 2C influx through Ca V 3.3 T-type channels (but not through Ca V 3.1 or Ca V 3.2 channels), which activates PKC-b and stimulates proliferation of cancer cells.…”