Voltage-Dependent Conductances in Cephalopod Primary Sensory Hair Cells

• Published in: Journal of neurophysiology Vol. 78; no. 6; pp. 3125 - 3132
• Main Authors: Chrachri, Abdesslam, Williamson, Roddy
• Format: Journal Article
• Language: English
• Published: United States Am Phys Soc 01.12.1997
• Subjects: Animals; Decapodiformes - physiology; Electric Conductivity; Eledone cirrhosa; Female; Hair Cells, Auditory - physiology; Loligo forbesi; Male; Marine; Microelectrodes; Octopodiformes - physiology; Patch-Clamp Techniques; Sensory Receptor Cells - physiology
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.1997.78.6.3125

Abdesslam Chrachri 1 and Roddy Williamson 1 , 2 1  The Marine Biological Association of the United Kingdom, The Laboratory, Citadel Hill, Plymouth PL1 2PB; and 2  Department of Biology, University of Plymouth, Plymouth PL4 8AA, United Kingdom Chrachri, Abdesslam and Roddy Williamson. Voltage-dependent conductances in primary sensory hair cells. J. Neurophysiol. 78: 3125-3132, 1997. Cephalopods, such as sepia, squid, and octopus, show a well-developed and sophisticated control of balance particularly during prey capture and escape behaviors. There are two separate areas of sensory epithelium in cephalopod statocysts, a macula/statolith system, which detects linear accelerations (gravity), and a crista/cupula system, which detects rotational movements. The aim of this study is to characterize the ionic conductances in the basolateral membrane of primary sensory hair cells. These were studied using a whole cell patch-clamp technique, which allowed us to identify five ionic conductances in the isolated primary hair cells; an inward sodium current, an inward calcium current, and three potassium outward currents. These outward currents were distinguishable on the basis of their voltage-dependence and pharmacological sensitivities. First, a transient outward current ( I A ) was elicited by depolarizing voltage steps from a holding potential of 60 mV, was inactivated by holding the cell at 40 mV, and was blocked by 4-aminopyridine. A second, voltage-sensitive, outward current with a sustained time course was identified. This current was not blocked by 4-aminopyridine nor inactivated at a holding potential of 40 mV and hence could be separated from I A using these protocols. A third outward current that depended on Ca 2+ entry for its activation was detected, this current was identified by its sensitivity to Ca 2+ channel blockers such as Co 2+ and Cd 2+ and by the N-shaped profile of its current-voltage curve. Inward currents were studied using cesium aspartate solution in the pipette to block the outward currents. Two inward currents were observed in the primary sensory hair cells. A fast transient inward current, which is presumably responsible for spike generation. This inward current appeared as a rapidly activating inward current; this was strongly voltage dependent. Three lines of evidence suggest that this fast transient inward current is a Na + current ( I Na ). First, it was blocked by tetrodotoxin (TTX); second, it also was blocked by Na + -free saline; and third, it was inactivated when primary hair cells were held at a potential more than 40 mV. The sustained inward current was not affected by TTX and was increased in amplitude 5 min after equimolar Ba 2+ replaced Ca 2+ as a charge carrier. This inward current also was blocked after external application of 2 mmol/l Co 2+ or Cd 2+ . Furthermore, this current was reduced significantly in a dose-dependent manner by nifedipine, suggesting that it is an L-type Ca 2+ current ( I Ca ).