Components of depolarization-induced transmembrane ion current in isolated smooth muscle cells of the guinea pigtaenia coli

Abstract

Transmembrane ion currents in isolated single smooth muscle cells (SMC) from the guinea pig taenia coli were investigated using a whole-cell mode of the patch-clamp technique. Currents induced by depolarizing shifts in the membrane potential from its holding level of --60 mV contained an initial inward phase (Ca 2+ current), which in 30-40 msec was followed by an outward phase. It was shown that outward current was carried by K ions and consisted at least of three components: one CaZ+-lndependent K + current of delayed rectifier (KV) and two Ca2+-dependent K + currents. The latter can be further divided into the apamin-sensitive (SK) and charybdotoxinsensitive (BK) currents. It was found that relative contributions of these three components in total outward current at 0 mV were 35-45%, 5-15%, and 45-55% for KV, SK, and BK currents, respectively. A potential-dependent current carried by CI ions was also found. This CI-current had inward direction within the range of potentials below the chloride equilibrium potential (EO) and outward direction above the Eel. The magnitude of Ci" current was significantly lower than the magnitude of total K + current.

Characteristics of paxilline-sensitive calcium-dependent potassium current in isolated intestine myocytes

“…4C). This observation is also indicative of the dependence of the paxilline-sensitive component of potassium current on the [Ca 2+ ] i ; in addition, a "pure" paxilline-sensitive current, whose values were obtained by subtraction of values of the current under the action of the blocker from control values, demonstrates the kinetics of activation similar to those for I Ca passed through L-type calcium channels [15,32]. The well-known blocker of voltage-dependent potassium channels TEA, when applied in a 1.0 mM concentration, suppressed outward currents evoked by shifts of the membrane potential from the holding level of -60 to +50 mV by more than 50%.…”

“…As is known, Со 2+ is an effective blocker of voltage-dependent calcium channels providing the entry of Са 2+ ions into cell [15,22]. When a solution containing an equimolar amount of Co 2+ instead of Сa 2+ was applied to SMCs, we observed a considerable depression of outward current.…”

“…At present, there are no highly selective blockers for this channel type. Earlier, it was found that under normal conditions more than 50% of the outward ion current evoked by step depolarization goes through Ca-activated potassium channels [15]. The main contribution to this current is provided by BK Са channels.…”

Mechanisms of non-adrenergic non-cholinergic synaptic transmission in smooth muscle cells of the gastrointestinal tract

“…Later, apamin has been shown to block specifically low-conductance Ca2 § potassium channels [17,18]. Taking this into account, apamin became a very useful and effective tool to study the participation of this type of potassium channels in the hyperpolarizing effects of neurotransmitters and other biologically active substances.…”