Calcium is necessary for light excitation in barnacle photoreceptors.
Illumination of barnacle (Balanus amphitrite) photoreceptors is known to increase the membrane permeability to sodium and Ca2+ ions resulting in a depolarizing receptor potential. In this report, we show that lanthanum (La3+), a known inhibitor of Ca-binding proteins, reversibly eliminates the receptor potential of barnacle photoreceptors when applied to the extracellular space. Similar reversible elimination of the light response was obtained by removing extracellular Ca2+ by application of the calcium chelating agent EGTA. Iontophoretic injection of Ca2+, but not K+ into the cells protected both the transient and the steady-state phases of the receptor potential from elimination by EGTA while only the transient phase was protected in the presence of La3+. The EGTA experiments suggest that internal Ca2+ is necessary for light excitation of barnacle photoreceptors while the La3+ experiments suggest that La(3+)-sensitive inward current is necessary to maintain excitation during prolonged light.
Werner
U
U
Department of Physiology, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
Suss-Toby
E
E
Rom
A
A
Minke
B
B
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002463:Cell Membrane Permeability; D004533:Egtazic Acid / Q000494:pharmacology; D007811:Lanthanum / Q000494:pharmacology; D008027:Light; D010775:Photic Stimulation; D010786:Photoreceptor Cells / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D015398:Signal Transduction / Q000502:physiology; D001468:Thoracica / Q000502:physiology*
D004533:Egtazic Acid; D007811:Lanthanum; D011188:Potassium; D002118:Calcium