Sodium-dependent Potassium Channels in Leech P Neurons

Abstract

In leech P neurons the inhibition of the Na(+)-K(+) pump by ouabain or omission of bath K(+) leaves the membrane potential unaffected for a prolonged period or even induces a marked membrane hyperpolarization, although the concentration gradients for K(+) and Na(+) are attenuated substantially. As shown previously, this stabilization of the membrane potential is caused by an increase in the K(+) conductance of the plasma membrane, which compensates for the reduction of the K(+) gradient. The data presented here strongly suggest that the increased K(+) conductance is due to Na(+)-activated K(+) (K(Na)) channels. Specifically, an increase in the cytosolic Na(+) concentration ([Na(+)](i)) was paralleled by a membrane hyperpolarization, a decrease in the input resistance (R(in)) of the cells, and by the occurrence of an outwardly directed membrane current. The relationship between R(in) and [Na(+)](i) followed a simple model in which the R(in) decrease was attributed to K(+) channels that are activated by the binding of three Na(+) ions, with half-maximal activation at [Na(+)](i) between 45 and 70 mM. At maximum channel activation, R(in) was reduced by more than 90%, suggesting a significant contribution of the K(Na) channels to the physiological functioning of the cells, although evidence for such a contribution is still lacking. Injection experiments showed that the K(Na) channels in leech P neurons are also activated by Li(+).

An annotated CNS transcriptome of the medicinal leech, Hirudo verbana: De novo sequencing to characterize genes associated with nervous system activity

“…A persistent cesium-sensitive inward current, potentially carried by IRK , has also been characterized in cultured R cells with voltage-clamp measurements during pharmacological blockade [ 53 ]. The dynamics of the Na + -activated K + channel KCNT have been examined in leech P cells where membrane resistance was strongly influenced by changes in outwardly directed membrane current with changing intracellular Na + concentration [ 54 ].…”

Slack, Slick, and Sodium-Activated Potassium Channels

“…The existence and general properties of K Na currents have been relatively well conserved throughout evolution and have been extensively studied in larval lamprey spinal cord neurons [24–28]. They have been described in a wide variety of neurons in the nervous system of invertebrates, including antennal-lobe neurons of the sphinx moth, Manduca sexta [29], Kenyon cells of mushroom bodies in crickets [30], pressure P neurons in the leech [31] and, bag cell neurons that regulate reproductive behavior in the sea hare Aplysia californica [32]. …”

Functional properties and cell type specific distribution ofIh channels in leech neurons

“…For leech HN cells, and briefly for Retzius and P neurons, I h has been described before (Angstadt, 1999;Angstadt and Calabrese, 1989;Arbas and Calabrese, 1987b;Coulon et al, 2008;Klees et al, 2005). However, a detailed description of the distribution and biophysical properties of leech I h across cell types was lacking.…”

“…I h was reported to play a role in stabilising the resting membrane potential in thalamic relay neurons,1999; Coulon et al, 2008). Marked voltage sags have been described in pressure (P) neurons in situ (Jansen and Nicholls, 1973;Klees et al, 2005), but the underlying mechanism has not been investigated. I h was also found in salivary glands of the giant Amazon leech, Haementeria ghilianii (Wuttke and Berry, 1992).…”