Smooth muscle sparklet Ca(v) channels defined: 1.2 is the number

Hydrogen sulfide activates Ca²⁺ sparks to induce cerebral arteriole dilatation

Hydrogen sulfide (H₂S) is a gaseous vasodilator produced by endothelial cells. Mechanisms by which H₂S induces vasodilatation are unclear. We tested the hypothesis that H₂S dilates cerebral arterioles by modulating local and global intracellular Ca²⁺ signals in smooth muscle cells. High-speed confocal imaging revealed that Na₂S, an H₂S donor, increased Ca²⁺ spark frequency ∼1.43-fold and decreased global intracellular Ca²⁺ concentration ([Ca²⁺]i) by ∼37 nM in smooth muscle cells of intact piglet cerebral arterioles. In contrast, H₂S did not alter Ca²⁺ wave frequency. In voltage-clamped (-40 mV) cells, H₂S increased the frequency of iberiotoxin-sensitive, Ca²⁺ spark-induced transient Ca²⁺-activated K⁺ (KCa) currents ∼1.83-fold, but did not alter the amplitude of these events. H₂S did not alter the activity of single KCa channels recorded in the absence of Ca²⁺ sparks in arteriole smooth muscle cells. H₂S increased SR Ca²⁺ load ([Ca²⁺]SR), measured as caffeine (10 and 20mM)-induced [Ca²⁺]i transients, ∼1.5-fold. H₂S hyperpolarized (by ∼18 mV) and dilated pressurized (40 mmHg) cerebral arterioles. Iberiotoxin, a KCa channel blocker, reduced H₂S-induced hyperpolarization by ∼51%. Iberiotoxin and ryanodine, a ryanodine receptor channel inhibitor, reduced H₂S-induced vasodilatation by ∼38 and ∼37%, respectively. In summary, our data indicate that H₂S elevates [Ca²⁺]SR, leading to Ca²⁺ spark activation in cerebral arteriole smooth muscle cells. The subsequent elevation in transient KCa current frequency leads to membrane hyperpolarization, a reduction in global [Ca²⁺]i and vasodilatation.

Glutamate regulates Ca2+ signals in smooth muscle cells of newborn piglet brain slice arterioles through astrocyte- and heme oxygenase-dependent mechanisms

Glutamate is the principal cerebral excitatory neurotransmitter and dilates cerebral arterioles to match blood flow to neural activity. Arterial contractility is regulated by local and global Ca(2+) signals that occur in smooth muscle cells, but modulation of these signals by glutamate is poorly understood. Here, using high-speed confocal imaging, we measured the Ca(2+) signals that occur in arteriole smooth muscle cells of newborn piglet tangential brain slices, studied signal regulation by glutamate, and investigated the physiological function of heme oxygenase (HO) and carbon monoxide (CO) in these responses. Glutamate elevated Ca(2+) spark frequency by approximately 188% and reduced global intracellular Ca(2+) concentration ([Ca(2+)](i)) to approximately 76% of control but did not alter Ca(2+) wave frequency in brain arteriole smooth muscle cells. Isolation of cerebral arterioles from brain slices abolished glutamate-induced Ca(2+) signal modulation. In slices treated with l-2-alpha-aminoadipic acid, a glial toxin, glutamate did not alter Ca(2+) sparks or global [Ca(2+)](i) but did activate Ca(2+) waves. This shift in Ca(2+) signal modulation by glutamate did not occur in slices treated with d-2-alpha-aminoadipic acid, an inactive isomer of l-2-alpha-aminoadipic acid. In the presence of chromium mesoporphyrin, a HO blocker, glutamate inhibited Ca(2+) sparks and Ca(2+) waves and did not alter global [Ca(2+)](i). In isolated arterioles, CORM-3 [tricarbonylchloro(glycinato)ruthenium(II)], a CO donor, activated Ca(2+) sparks and reduced global [Ca(2+)](i). These effects were blocked by 1H-(1,2,4)-oxadiazolo-(4,3-a)-quinoxalin-1-one, a soluble guanylyl cyclase inhibitor. Collectively, these data indicate that glutamate can modulate Ca(2+) sparks, Ca(2+) waves, and global [Ca(2+)](i) in arteriole smooth muscle cells via mechanisms that require astrocytes and HO. These data also indicate that soluble guanylyl cyclase is involved in CO activation of Ca(2+) sparks in arteriole smooth muscle cells.

The KCNMB1 Glu65Lys polymorphism associates with reduced systolic and diastolic blood pressure in the Inter99 study of 5729 Danes

OBJECTIVE

The large Ca2+ and voltage-dependent potassium channel is important in regulating vascular tone in smooth muscle tissue. The rs11739136 KCNMB1 Glu65Lys polymorphism in the beta1 subunit of the Ca2+ and voltage-dependent potassium channel has, in some studies, been reported to associate with a protective effect on diastolic hypertension. The previous studies have, however, been conflicting, and the aim of the present study was to clarify the impact of the Glu65Lys polymorphism on hypertension at the population level of middle-aged people.

DESIGN

Large-scale sex-stratified case-control studies and analyses of quantitative blood pressure.

METHODS

The KCNMB1 Glu65Lys (rs11739136) polymorphism was genotyped in 5729 Danes using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of PCR-generated primer extension products.

RESULTS

In the population-based Inter99 cohort, the Glu65Lys polymorphism was associated with a 1.3% decrease in systolic blood pressure (P=0.01) and a 1.1% decrease in diastolic blood pressure (P=0.04) per Lys-allele among 2668 men. Among women, we observed no association between systolic or diastolic blood pressure and the Glu65Lys polymorphism.

CONCLUSION

If replicated, our findings suggest that the KCNMB1 Glu65Lys polymorphism associates with reduced systolic and diastolic blood pressure in middle-aged men.