Rhythmic contractions in isolated small arteries of rat: role of K⁺ channels and the Na⁺, K⁺‐pump

Abstract

Small mesenteric arteries from Wistar rats display rhythmic tension oscillations, associated with oscillations in membrane potential, when stimulated with noradrenaline. The purpose of this study was to investigate the role of potassium conductance and Na+, K(+)-pump activity in the generation of these oscillations. The effect on the rhythmic contractions of several agents, interacting with K+ channels, was studied. Application of apamin, pinacidil or glibenclamide did not affect the rhythmic activity. Tetraethylammonium (TEA) increased the frequency of the rhythmic contractions, while application of 4-aminopyridine (4-AP) increased the amplitude by approximately 50%, with no changes in frequency. Ba2+, on the other hand, impaired the rhythmic contractions or converted them to irregular oscillations in the presence of functional endothelium, but did not affect oscillations in endothelium-denuded vessels. Ouabain or exposure to K(+)-free solution, procedures known to inhibit the Na+,K(+)-pump, abolished the rhythmic contractions. This effect was immediate, suggesting that it was due to elimination of the electrogenic action of the Na+,K(+)-ATPase, rather than to a change in intracellular ion concentrations. Exposure to an extracellular potassium concentration of more than 20 mM also inhibited the oscillation activity. The results suggest that the oscillations are not caused by, but may be modulated by, variations in potassium conductance. The Na+,K(+)-pump seems to play an important role in the generation of rhythmic contractions in these vessels.

Essential role of EDHF in the initiation and maintenance of adrenergic vasomotion in rat mesenteric arteries

“…The inability of IbTX to substitute for ChTX thus ruled out the involvement of BK Ca channels. Vasomotion persisted in the presence of TEA (10 mM) or 4-aminopyridine (4-AP; 1-5 mM) (15,17). In our system, 5 mM 4-AP did not abolish vasomotion in arteries stimulated with 10.0 M PE (n ϭ 2).…”

The α2 isoform of the Na,K-pump is important for intercellular communication, agonist-induced contraction, and EDHF-like response in rat mesenteric arteries

“…In blood vessels ouabain increases myogenic tone (53), inhibits intercellular communication and thus vasomotion (19,28,31), and reduces the EDHF response (12). It has been suggested that inhibition of the ␣ 2 isoform is responsible for these effects.…”

Differential activation of ion channels by inositol 1,4,5‐trisphosphate (IP3)‐ and ryanodine‐sensitive calcium stores in rat basilar artery vasomotion

“…Paradoxically, studies of cultured SMCs and of pressurized cerebral arteries have demonstrated an important role for intracellular ryanodine sensitive calcium stores and potassium channels in relaxation of cerebral vessels (Nelson et al 1995;Bonev et al 1997;Gollasch et al 1998;Jaggar, 2001;Perez et al 2001). Modulation of agonist-induced vasomotion by potassium conductances has also been demonstrated in the rat mesenteric artery (Gustafsson & Nilsson, 1994). Since control of blood flow through cerebral vessels varies in several respects from that in systemic vessels (Faraci & Heistad, 1998) we were interested to investigate the role of intracellular stores in the mechanisms underlying cerebral vasomotion.…”