L-glutamate-induced responses and cGMP-activated channels in three subtypes of retinal bipolar cells dissociated from the cat.
Effects of L-glutamate (Glu), the neurotransmitter released by photoreceptors, on isolated cat bipolar cells were examined. Membrane currents of bipolar cells were recorded by the patch-clamp technique in a conventional whole-cell recording configuration using pipettes containing 1 mM cGMP, which has been known to activate a cationic current sensitive to Glu in ON-type bipolar cells. ON-type bipolar cells (depolarized by light in in situ) and OFF-type bipolar cells (hyperpolarized by light) were identified by their response polarity to Glu. When the whole-cell configuration was established, ON-type bipolar cells showed a steady inward current which was suppressed by Glu, consistent with the response polarity observed in in situ recordings. In contrast, OFF-type cells did not show a steady current during the recordings. However, they responded to Glu with an increase in cationic conductance. Among recorded cells, rod-driven bipolar cells were identified by their immunoreactivity to anti-protein kinase C (PKC-IR) antibody. Examination of PKC-IR revealed that ON-type bipolar cells included both rod- and cone-driven bipolar cells, while OFF-type cells were all cone-driven bipolar cells. The cGMP-activated current observed in ON-type cells was accompanied by a change in the current fluctuation due to the opening and closing of underlying channels. Fluctuation analysis gave a unitary conductance value of 13 pS. In half of the cells examined, maximum open probability reached almost 100%. The cGMP-activated channel in bipolar cells seems novel, fundamentally different from those found in photoreceptor cells or olfactory receptor cells.
de la Villa
P
P
Department of Information Physiology, National Institute for Physiological Sciences, Okazaki, Japan.
Kurahashi
T
T
Kaneko
A
A
D000818:Animals; D002415:Cats; D002478:Cells, Cultured; D006152:Cyclic GMP / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D018698:Glutamic Acid / Q000494:pharmacology*; D007150:Immunohistochemistry; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D010786:Photoreceptor Cells; D011493:Protein Kinase C / Q000032:analysis / Q000378:metabolism*; D012160:Retina / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology / Q000502:physiology; D017948:Retinal Rod Photoreceptor Cells / Q000166:cytology / Q000502:physiology; D013997:Time Factors
D007473:Ion Channels; D018698:Glutamic Acid; D011493:Protein Kinase C; D006152:Cyclic GMP