The Chemical Modification of KCa Channels by Carbon Monoxide in Vascular Smooth Muscle Cells

Abstract

The chemical modification of big conductance calcium-activated potassium (K Ca ) channels in rat tail artery smooth muscle cells by carbon monoxide (CO) was investigated using the cell-free single channel recording technique. Exposure of the internal surface of cell membranes to diethyl pyrocarbonate (DEPC) neither affected the characteristics of K Ca channels nor modified the stimulatory effect of CO on K Ca channels. However, when DEPC was applied to the external surface of cell membranes, the open probability of K Ca channels was reduced. The pH and concentration dependence of the effect of DEPC indicated the specific modification of histidine residues. Kinetic analysis suggested that one externally located histidine residue was modified by DEPC. Treatment of the external surface of cell membranes with DEPC abolished the CO-induced increase in the open probability of K Ca channels. Likewise, the presence of CO partially protected K Ca channels from inhibition by DEPC. Moreover, photooxidation of the histidine residue located on the external membrane surface abolished the CO-induced activation of K Ca channels. Our study demonstrates that the CO-induced increase in the open probability of K Ca channels may rely specifically on the structure and topological locations of histidine residues.The presence of both inducible and constitutive forms of heme oxygenase, which cleave the heme ring to form carbon monoxide (CO), 1 has been demonstrated in vascular smooth muscle cells (1). Direct measurement of the endogenous production of CO from vascular smooth muscle cells has also recently been realized (2). Our previous study (3), as well as those of others (4 -6), demonstrated the regulatory function of CO in various types of vascular tissues. For example, CO relaxed precontracted rat tail artery strips in a concentration-dependent manner (3). This effect of CO was mediated partially by a cGMP signaling pathway and partially by calcium-activated K (K Ca ) channels. Using the single channel recording patch-clamp technique, we found that CO increased the open probability (NPo) of K Ca channels. 2 This effect of CO may be caused by a direct interaction between CO and K Ca channels as the activities of the cGMP pathway and G proteins are not involved in the activation of K Ca channels by CO. To date, the mechanism by which CO directly affects K Ca channels remains unclear.The electrical properties of K Ca channels are determined by different amino acid residues that are constitutive components of the channel protein. The primary structure of K Ca channels in several cell types, excluding vascular smooth muscle cells, is known, but the functional roles of various amino acids in the gating and conducting of K Ca channels are still in question. Limited studies show that the modification of one or more amino acid residues may significantly change the conductance and/or NPo of K Ca channels (7-9). Both synthetic chemical reagents and some simple biological active molecules such as nitric oxide (7) and hydrogen peroxide (10) can...

The RCK1 high-affinity Ca 2+ sensor confers carbon monoxide sensitivity to Slo1 BK channels

“…This finding is consistent with an earlier suggestion that histidine may be important (26), although the original study implicated extracellularly accessible histidine residues. The reason for the histidine requirement is not entirely clear.…”

“…A previous study has implicated the importance of extracellularly accessible histidine residues in the overall stimulatory effect of CO on native vascular BK channels (26). We found that pretreatment of the Slo1 channel with the histidine modifier diethyl pyrocarbonate (DEPC) applied intracellularly eliminated the stimulatory action of CO ( Fig.…”

“…Increasing evidence shows that CO stimulates the Slo1 BK channel without any requirement for cytoplasmic signaling cascades (16,26). However, the biophysical and molecular mechanisms underlying the stimulatory action of CO remained unresolved.…”

Pancreatic islet overproduction of H2S and suppressed insulin release in Zucker diabetic rats

“…With a holding potential of À60 mM and in the absence of Ca 2 þ from the bath solution, neither voltage-dependent K þ channel nor calcium-activated K þ channels would have been activated. 26,27 H 2 S at 100 mM significantly increased K ATP channel currents that were subsequently inhibited by gliclazide (1 mM), a classical K ATP channel blocker, 28,29 in b-cells from both ZL (Figure 7a) and ZDF rats (Figure 7b). The amplitude of K ATP channel cur- rents at resting condition appeared to be lower in ZDF b-cells than ZL b-cells (Figure 7c).…”

The carbon monoxide donor, CORM-2, is an antagonist of ATP-gated, human P2X4 receptors

“…There are many proposed cellular targets of CO including soluble guanylate cyclase (sGC) [24] and mitogen-activated protein kinases (for review, see [25]). Recent experiments have also shown CO to play important roles in cardiovascular function [26] and O 2 sensing [27,28] via an activation of large-conductance, calcium-activated potassium channel (BK Ca ). Other ion channels have also been shown to be modulated by CO such as L-type calcium channels (Ca v 1.2) [29], TREK-1 [30] and ENaC channels [31].…”