Ca2+-Activated K+-Channels from Isolated Type I Carotid Body Cells of the Neonatal Rat

Abstract

1. Ca2+-activated K+ (KCa) channels in neonatal rat type I carotid body cells were studied using single channel patch clamp techniques. In outside-out patches, using symmetrical 120 mm [K+] solutions, channels were observed with a slope conductance of 190 pS and a reversal potential of 0 mV. Reducing [K+]0 to 5 mm shifted the reversal potential as expected for a K+-selective channel.2. With 100 nM Ca2+ bathing the cytosolic aspect of patches, channel activity (number of active channels in a patch x open probability, NP0) increased with depolarization. NPo also increased with increasing 'cytosolic' [Ca2+] at a fixed membrane potential (0 mV). Using outside-out patches, bath application of 20 or 100 nM charybdotoxin reduced NPo by >85 %. These data indicate the presence of K+a channels in type I cells.3. At 0 mV, using solutions of identical composition (1 /M Ca2+ bathing the cytosolic aspect of the channels), NPo was higher in outside-out patches than in inside-out patches. NPo was greatest in recordings using the perforated-vesicle technique. 4. Hypoxia and anoxia were without effect on Kta channels in outside-out patches, but caused significant, reversible reductions of NPo in channels recorded in perforated vesicles. 5. The whole-cell perforated-patch technique was used to record membrane potential at 35-37 'C. Hypoxia, anoxia and charybdotoxin all depolarized type I cells. 6. Our results suggest an important role for Ka channels in type I carotid body cells, and their activity in relation to a model for chemotransduction is discussed.

Cellular properties and chemosensory responses of the human carotid body

“…Our study also suggests the presence of maxi‐K + channels in human glomus cells. These channels have been shown to be important for chemotransduction in rat CB cells (Wyatt & Peers, 1995). Glomus cells of lower mammals contain several background K + channels that contribute to a high K + resting permeability (see Ortega‐Sáenz et al 2010 and references therein).…”

AMP‐activated protein kinase underpins hypoxic pulmonary vasoconstriction and carotid body excitation by hypoxia in mammals

“…Upon exposure to hypoxia, voltage‐gated Ca 2+ influx into type I cells, rather than ER Ca 2+ release (Buckler & Vaughan‐Jones, 1994), initiates neurosecretion (Fidone et al 1988; Gonzalez et al 1994; Chen et al 1997) and thereby increases sensory afferent discharge to the brainstem. This process is driven by the inhibition of what have been termed O 2 ‐sensitive K + channels (Lopez‐Barneo et al 1988; Peers, 1990; Stea & Nurse, 1991; Lopez‐Lopez & Gonzalez, 1992; Wyatt & Peers, 1992, 1995; Buckler, 1997, 1999; Buckler et al 2000). Consistent with this, immunofluorescence imaging revealed that the AMPK‐α1 catalytic subunit isoform expressed in carotid body type I cells was almost entirely (∼75%) restricted to a volume within 1 μm of the plasma membrane.…”

“…Consistent with AMPK‐α1 being targeted to the plasma membrane in carotid body type I cells, AMPK activation by AICAR, like hypoxia, induced a reversible depolarization of the membrane potential (Wyatt et al 2006). Perhaps most significantly, like hypoxia (Wyatt & Peers, 1995; Buckler et al 2000), AMPK activation (Wyatt et al 2006) elicited depolarization of rat carotid body type I cells by inhibiting O 2 ‐sensitive K + currents carried by the TASK (TWIK‐related acid‐sensitive potassium)‐like leak K + channels and large‐conductance Ca 2+ ‐activated K + channels (BK Ca ), but not by inhibiting the O 2 ‐insensitive voltage‐gated K + channel (Kv) current. Consequently, an increase in the intracellular Ca 2+ concentration was evoked via Ni 2+ ‐ and Cd 2+ ‐sensitive voltage‐gated Ca 2+ influx pathways, which ultimately led to an increase in sensory afferent discharge from the isolated carotid body (Evans et al 2005; Wyatt et al 2006).…”

Detecting acute changes in oxygen: will the real sensor please stand up?

“…Indeed, there have been almost as many candidate O 2 sensors as there are experimental strategies with which to probe their nature. Moreover, the membrane hypothesis itself has been challenged by at least two independent observations showing the requirement for cytosolic factors in hypoxic K + channel inhibition (Wyatt & Peers, 1995; Buckler, 1997). However, over the last decade or so, it has become clear that there is unlikely to be a unifying mechanism to account for O 2 sensing in all tissues, and it is probable that there may not even be a single sensing system within each cell type.…”

“…In the rat, there is clear difference of opinion, with either a voltage‐activated, Ca 2+ ‐sensitive, large‐conductance (BK Ca ) or an open‐rectifying, acid‐sensitive member of the tandem P domain K + channel family (TASK) being implicated in the fundamental process of O 2 sensing. Evidence for BK Ca channels comes from whole‐cell (Peers, 1990; Wyatt & Peers, 1995) and excised patch‐clamp data (Riesco‐Fagundo et al 2001) from isolated glomus cells and complementary amperometric data from intact carotid body slices (Pardal et al 2000). Suggestions of a background, leak K + channel‐dependent O 2 sensitivity have been substantiated by patch‐clamp data in isolated rat glomus cells (Buckler, 1997) and supported by in situ hybridization employing a probe to the K + channel, TASK1 (Buckler et al 2000).…”