Characterization of an ATP‐modulated large conductance Ca(2+)‐activated K+ channel present in rat cortical neurones.

Abstract

1. Single channel current recordings were used to study the characteristics of a large conductance Ca2+-activated K+ (BKCa) channel present in neurones acutely dissociated from the rat motor cortex. Application of ATP to the intracellular surface of excised inside-out patches produced a large, concentration-dependent increase in BKCa channel activity.2. This ATP-mediated activation was dependent upon the presence of Mg2+ in the intracellular bathing solution and was diminished by the phosphatases 2,3-butanedione monoxime (BDM) or alkaline phosphatase and by the protein kinase inhibitors staurosporine, H-7 and PKI.3. ADP stimulated BKCa channel activity in a Mg2+-dependent manner, an action also inhibited by the concomitant application of PKI or BDM. The effect of ADP was reduced by application of hexokinase and glucose or by application of the adenylate kinase inhibitor Ap5A.4. Of other nucleotides tested, only CTP consistently activated BKca channel activity.5. Using the cell-attached configuration, bath application of forskolin or dibutyryl cAMP stimulated BKCa channel activity. 6. It is concluded that BKCa channel activity in the rat motor cortex is subject to modulation by the activity of a closely associated kinase. The ability of cAMP activators to stimulate BKCa channel activity in the intact cell suggests that this system may be of physiological importance.Large conductance Ca2+-activated K+ (BKCa) channels have been identified in many cell types including neurones, smooth and skeletal muscle, kidney tubules, and both endocrine and exocrine glands (Latorre, Oberhauser, Labarca & Alvarez, 1989). Although the precise role of these channels is not clear, they have been implicated in a number of important physiological processes such as the regulation of secretion from endocrine and exocrine glands, the co-ordination of membrane excitability in neurones and the control of K+ ion movement across epithelia.The regulation of BKCa channel activity is complex, with both a rise in intracellular Ca2+ and membrane depolarization producing an increase in channel activity. Additionally, it has recently been shown that conditions which favour protein phosphorylation can also enhance BKca channel activity in a number of tissues (Sadoshima, Akaike, Kanaide & Nakamura, 1988; Kume, Takei, Tokuno & Tomita, 1989). However, the most widely studied example of BKCa channel regulation by phosphorylation has been obtained using synaptosomal membranes from the rat brain incorporated into lipid bilayers (Farley & Rudy, 1988 P(r) = 100 n! pr(l _ p)n r r!(n -r)! where P(r) is the percentage time that 0, 1, 2... n channels are open, n is the total number of channels in the membrane patch, r is the number of channels open and p is the probability that anygiven channel is open.In order to assess the pH sensitivity of BKca channel activity, the data obtained in the presence of varying conditions of intracellular pH were fitted by non-linear regression to the following equation:where P. is the channel activity at the test pH, pK is the ...

Metabotropic Glutamate Receptor Activation Enhances the Activities of Two Types of Ca2+-Activated K+Channels in Rat Hippocampal Astrocytes

“…The K Ca channels are important regulators of arterial muscle reactivity and the development of pressure-induced myogenic constriction in the cerebral circulation and in other arterial beds (Brayden and Nelson, 1992;Gebremedhin et al, 1992;Nelson and Quayle, 1995;Gebremedhin et al, 1996), whereas in neuronal cells they contribute to coordination of membrane excitability (Lee et al, 1995) and to regulation of the resting potential and control of spontaneous impulse generation (Johansson et al, 2001). In presynaptic nerve terminals, K Ca channels are colocalized with voltage-dependent Ca 2ϩ channels and have been suggested to play a critical role in the regulation of transmitter release (Marrion and Tavalin, 1998).…”

“…The K Ca channels are ubiquitous in a variety of tissue types and are involved in diverse physiological functions. Thus, vascular smooth muscle K Ca channels are important regulators of vascular tone (Brayden and Nelson, 1992;Gebremedhin et al, 1992), and in neuronal cells they contribute to membrane excitability (Lee et al, 1995). In the presynaptic terminals, K Ca channels are colocalized with voltage-dependent Ca 2ϩ channels and play a critical role in the regulation of transmitter release (Lee et al, 1995).…”

Modulation of the Ca2+-Activated Large Conductance K+ Channel by Intracellular pH in Human Renal Proximal Tubule Cells.

“…Furthermore, we attempted to explore the mechanism of pH i -sensitivity of this BK channel with kinetic analysis and to characterize the pH i -mediated channel gating. It had been shown in some reports that lowering pH i reduced the conductance of BK channels and that raising pH i enhanced it besides the pH i effect on channel activity [9,15,20]. However, changes in pH i induced no significant effect on the conductance of the BK channels in RPTECs (Fig.…”

“…Besides Ca 2ϩ and voltage, other factors such as ATP [8-11], pH [8, 9, 12-21], and Mg 2ϩ [19,[22][23][24] were also reported to modulate BK channels. Among these factors, intracellular pH (pH i ) is one of the significant factors that affect channel activity [8,9,[12][13][14][15][16][17][18][19][20][21], i.e., channel activity is inhibited by intracellular acidification and stimulated by its alkalization. Although the mechanism for pH i effects on channel activity was not precisely understood, two different mechanisms have been proposed.…”

“…One is that an increased cytoplasmic H ϩ can compete with Ca 2ϩ in binding to the same sites, thereby inhibiting channel activity [14][15][16], whereas the other is that the pH i -mediated change in channel activity is not competitive with Ca 2ϩ [17]. Moreover, it was demonstrated that the conductance of some BK channels was reduced by lowering pH i and enhanced by raising it [9,15,20].In the renal tubules, BK channels have been reported in cultured rabbit proximal tubule cells [25] …”