Distinct Pathways of Ca ²⁺ Sensitization in Porcine Coronary Artery

Abstract

Abstract-Alterations of the Ca 2ϩ sensitivity of contraction have been reported for porcine coronary artery, but the mechanisms are not clearly understood. We investigated the mechanism(s) of Ca 2ϩ sensitization in response to the thromboxane A 2 analogue (U46619). Our hypothesis is that different mechanisms of Ca 2ϩ sensitization could be distinguished by their distinct time courses. Therefore, we measured the time course of [Ca 2ϩ ] i and isometric force simultaneously in an intact artery after a single addition of U46619. The initial transient phase was associated with Ca 2ϩ release from the sarcoplasmic reticulum, whereas the maintained phase was associated with Ca 2ϩ influx. Two distinct types of Ca 2ϩ sensitization characterized these phases with either protein kinase C (PKC)-mediated or Rho-kinasemediated mechanisms. Their effects were quite distinct on the basis of the time courses over which the sensitization was effective. PKC inhibition (1 mol/L calphostin C) had a much greater effect in the initial phase, diminishing the size of the transient and prolonging the rise in force and the decline in [Ca 2ϩ ] i . There were limited effects on the sustained force. Rho-kinase inhibition (10 mol/L Y27632), in contrast, nearly abolished the sustained force but had a lesser effect on the transient phase. Neither inhibitor had any effect on the force versus [Ca 2ϩ ] i relations for KCl contractures. Our evidence suggests that both PKC-mediated and Rho-kinase-mediated Ca 2ϩ sensitizations are present in coronary arteries, but the latter is dominant in thromboxane A 2 receptor-mediated contraction.

Vasorelaxing Effect of Hypoxia via Rho-kinase Inhibition on the Agonist-specific Vasoconstriction

“…Fluoride is also a classical Ser/Thr phosphatase inhibitor (Shenolikar and Nairn, 1991) and is routinely included in extraction buffers to prevent dephosphorylation of proteins on Ser and Thr residues by endogenous phosphatases. On the other hand, previous studies examining the mechanisms of thromboxane A 2 mimetic U46619-induced arterial contraction have reported variable findings with regard to the contraction related to Rho-kinase activation (Nobe and Paul, 2001;Tasaki, et al, 2003;Wilson, et al, 2005). Therefore, it was consistent with the possibility that the hypoxia could decrease fluoride-or thromboxane A 2 mimetic-induced contraction inhibiting Rho-kinase activity.…”

Vascular endothelin ETB receptor-mediated contraction requires phosphorylation of ERK1/2 proteins

“…A similar bimodal appearance has been described for the thromboxane A 2 analogue U46619-induced contraction in porcine coronary artery (Nobe and Paul, 2001). The transient phase of contraction to U46619 was associated with Ca 2+ release from the sarcoplasmic reticulum and a protein kinase C (PKC)-mediated Ca 2+ release, while in the sustained phase, involves Ca 2+ influx from the extracellular space and Rho-kinase-mediated Ca 2+ sensitization (Nobe and Paul, 2001). The present study has revealed that the ERK1/2 inhibitor SB386023 (10 5 M) and the calcium influx inhibitor, nifedipine, significantly decreased the sustained contraction.…”

“…The increase of intracellular calcium induced via endothelin ET B receptor activation consists of two phases: one rapid and one sustained. The rapid phase of calcium release induced by agonist via endothelin ET B receptors, is supposed to occur via the inositol 1, 4, 5-triphosphate [Ins(1, 4, 5)P3]-mediated calcium release from the sarcoplasmic reticulum (Nobe and Paul, 2001). This was, however, not inhibited by nifedipine or SB386023.…”

Rho kinase is involved in Ca2+ entry of rat penile small arteries

“…This is consistent with findings in tracheal smooth muscle (13) and in rat aorta and small mesenteric arteries (9) where Rho kinase regulates the Ca 2ϩ entry upon activation of muscarinic and ␣ 1 -adrenergic receptors, respectively. However, this involvement is probably dependent on the type of receptor and/or vascular bed since inhibition of Rho kinase did not significantly alter the Ca 2ϩ influx evoked by thromboxane A 2 in either porcine coronary artery (17) or pulmonary arteries (7).…”