Features of a calcium independent, caffeine sensitive outward current in single smooth muscle cells from guinea pig portal vein

Abstract

Using the single electrode voltage-clamp technique, vascular smooth muscle cells from the guinea pig portal vein showed an initial inward (Ca2+) current followed by an outward current which peaked within 100 ms and then declined to a steady level in a few seconds. Caffeine (1 mmol/l) selectively blocked the transient component of the outward current (ITO) and allowed differentiation of the outward current into two components: ITO and a caffeine resistant background current. The potassium channel blockers TEA (10 mmol/l) and 4-AP (5 mmol/l) produced about 90% suppression of ITO. ITO was identified as a calcium independent potassium current. Analysis of the inactivation and recovery from inactivation of ITO revealed similarities to the A-current first described for molluscan neurones (11) and later for crista terminalis of rabbit heart (4). Being much slower than this current it also bears similarities in its inactivation kinetics to a transient outward current identified in rabbit portal vein (2, 6).

Dual actions of caffeine on voltage-dependent currents and intracellular calcium in taste receptor cells

“…Quinine and forskolin act as direct blockers of potassium channels. Caffeine, too, has been reported to directly inhibit potassium channels in a number of cell types, including mammalian ventricular myocytes (48), vascular smooth muscle (38), dissociated chick autonomic ganglion neurons and pineal cells (43), and rat anterior pituitary cells (26). The biophysical properties of the caffeine-sensitive potassium channels are clearly different in these cells, suggesting a direct effect on conserved pore regions of the channel molecule.…”

Effects of cicletanine on whole‐cell currents of single smooth muscle cells from the guinea‐pig portal vein

“…This inward current then declined and reversed to become an outward current. The major part of outward current in these cells was also present in a calcium-free bathing solution (Noack et al, 1990). The family of current traces shown in Figure la illustrates the general voltage-dependency of the inwardly-and outwardly-directed current in this tissue.…”

Effects of caffeine and 3‐isobutyl‐1‐methylxanthine on voltage‐activated potassium currents in vertebrate neurones and secretory cells

“…A structurally related methylxanthine, IBMX, also caused inhibition of voltage-activated K+ currents in chick ciliary ganglion neurones at millimolar concentrations. Previous studies have shown that millimolar concentrations of caffeine inhibit voltage-dependent K+ currents in rat ventricular myocytes (Sanchez-Chapula, 1992;Varro et al, 1993) and guinea-pig portal vein (Noack et al, 1990), although these effects were not described in detail. IBMX has been shown to inhibit a voltage-activated tetraethylammonium-sensitive K+ current in rat sensory neurones (Usachev et al, 1995).…”

“…In this regard, there are data showing that millimolar concentrations of caffeine can inhibit voltage-dependent K+ currents in mammalian ventricular myocytes (Sanchez-Chapula, 1992;Varro et al, 1993) and vascular smooth muscle (Noack et al, 1990) as well as voltage-activated Na' channels in ventricular myocytes (Habuchi et al, 1991). To date, there have been no studies describing direct effects of caffeine on voltage-activated K+ channels in neurones or secretory cells, even though this compound is widely used in studies of those cell types (reviewed by Pozzan et al, 1994).…”