Barium ions inhibit the dynamic response of guinea-pig corneal cold receptors to heating but not to cooling.
An in vitro preparation of the guinea-pig cornea was used to study the effects of the K+ channel blockers 4-aminopyridine (4-AP), tetraethylammonium (TEA) and Ba2+ on nerve terminal impulses (NTIs) recorded extracellularly from cold sensory receptors. These receptors have an ongoing discharge of NTIs that is increased by cooling and decreased by heating. The K+ channel blocker 4-AP reduced the negative amplitude of the diphasic (positive-negative) NTIs, whereas TEA and Ba2+ prolonged the duration of the negative component. As the shape of the NTI is determined by the first derivative (dV/dt) of the membrane voltage change, these changes in the negative component are consistent with the blockade of K+ channels that contribute to action potential repolarization. Only TEA changed the basal activity of the receptors, increasing the likelihood of burst discharges. Ba2+ selectively reduced the response of the receptors to heating, whereas neither 4-AP nor TEA modified the response to heating or to cooling. The findings indicate that K+ channels blocked by 4-AP, TEA and Ba2+ contribute to action potential repolarization in corneal cold receptors, and that ionic mechanisms that underlie the reduction in NTI frequency in response to heating differ from those that increase activity in response to cooling.
Brock
James
J
Prince of Wales Medical Research Institute, Barker St, Randwick, NSW 2031, Australia. j.brock@unsw.edu.au
Acosta
M Carmen
MC
Al Abed
Amr
A
Pianova
Svetlana
S
Belmonte
Carlos
C
D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001464:Barium / Q000494:pharmacology*; D003080:Cold Temperature; D003315:Cornea / Q000294:innervation* / Q000502:physiology; D005260:Female; D006168:Guinea Pigs; D006358:Hot Temperature; D008297:Male; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D017729:Presynaptic Terminals / Q000187:drug effects / Q000502:physiology; D011984:Sensory Receptor Cells / Q000187:drug effects / Q000502:physiology; D019789:Tetraethylammonium / Q000494:pharmacology; D022722:Thermogenesis / Q000502:physiology; D013823:Thermoreceptors / Q000187:drug effects* / Q000502:physiology*
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D001464:Barium; D019789:Tetraethylammonium; D015761:4-Aminopyridine