Cobalt (Co2+) can mediate dynamic feedback signals driven by calcium (Ca2+) sensor molecules in mouse rod photoreceptors

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author F. Vinberg and A. Koskelainen Name of the publication Cobalt (Co2+) can mediate dynamic feedback signals driven by calcium (Ca2+) sensor molecules in mouse rod photoreceptors Publisher School of Science Unit Biomedical Engineering and Computational Science (BECS) Series Aalto University publication series SCIENCE + TECHNOLOGY 12/2011 Field of research Biophysics Abstract Calcium (Ca2+) controls negative feedback mechanisms that regulate the sensitivity of the rod photoreceptor cell to light. Ca2+ signals are mediated by calcium sensor proteins whose specificity against other ions under a natural cellular environment has rarely been studied. It is clear that these proteins must be very selective against magnesium (Mg2+) since they must function in cells under conditions where [Mg2+] exceeds [Ca2+] by a factor of ~104 – 105. Mg2+ is chemically very similar to Ca2+ but significantly smaller, and thus it is expected that also other small divalent cations can be discriminated by Ca2+ sensor proteins. We adopted an experimental protocol to study the specificity of the known Ca2+ sensor proteins, GCAP and recoverin, against some divalent cations in the intact rod photoreceptor cells with transretinal ERG technique. Surprisingly, we found that the small transition metal ion cobalt (Co2+) can mediate the negative feedback signals that are normally driven by changes in [Ca2+] in the rod outer segment.Calcium (Ca2+) controls negative feedback mechanisms that regulate the sensitivity of the rod photoreceptor cell to light. Ca2+ signals are mediated by calcium sensor proteins whose specificity against other ions under a natural cellular environment has rarely been studied. It is clear that these proteins must be very selective against magnesium (Mg2+) since they must function in cells under conditions where [Mg2+] exceeds [Ca2+] by a factor of ~104 – 105. Mg2+ is chemically very similar to Ca2+ but significantly smaller, and thus it is expected that also other small divalent cations can be discriminated by Ca2+ sensor proteins. We adopted an experimental protocol to study the specificity of the known Ca2+ sensor proteins, GCAP and recoverin, against some divalent cations in the intact rod photoreceptor cells with transretinal ERG technique. Surprisingly, we found that the small transition metal ion cobalt (Co2+) can mediate the negative feedback signals that are normally driven by changes in [Ca2+] in the rod outer segment.