scholarly journals Effect of Low Extracellular Calcium Concentration on Photosensittvity of Isolated Rods from Frog Retina

1989 ◽  
Vol 145 (1) ◽  
pp. 255-262
Author(s):  
KATSU AZUMA
Keyword(s):  
Calcium Concentration ◽  
Rana Catesbeiana ◽  
Light Sensitivity ◽  
Recovery Phase ◽  
Physiological Solution ◽  
Extracellular Calcium ◽  
Membrane Current ◽  
Peak Amplitude ◽  
Extracellular Calcium Concentration ◽  
Light Flashes

The effects of extracellular calcium concentration ([Ca2+]o) on the light sensitivity of isolated single rods from the retina of the frog (Rana catesbeiana) were investigated by sucking the rod inner segments into tightly fitting pipettes. Light flashes (500nm, 1s duration) evoked transient outward changes of membrane current (photoresponses). The peak amplitude of maximal photoresponses in normal physiological solution varied between 6 and 12 pA. Reducing ([Ca2+]o) from O.9μmmoll−1 (normal Ca2+) to 90μmoll−1 (low Ca2+) increased the peak amplitude of photoresponses and shortened the recovery phase of the responses. The effects of larger changes in light intensity were also investigated. After light-on there was a steady outward change of membrane current, and after lightoff the current recovered to the initial dark level. With a low external Ca2+ concentration, light-off induced a large inward change of membrane current which transiently overshot the initial dark level. During the overshoot stage, light flashes evoked photoresponses which were larger than those in the initial dark period.

scholarly journals Rare diseases caused by abnormal calcium sensing and signalling

Endocrine ◽  
2021 ◽  
Vol 71 (3) ◽  
pp. 611-617
Author(s):  
Judit Tőke ◽  
Gábor Czirják ◽  
Péter Enyedi ◽  
Miklós Tóth
Keyword(s):  
Calcium Homeostasis ◽  
Calcium Concentration ◽  
Gene Mutations ◽  
Cell Types ◽  
Bartter Syndrome ◽  
Extracellular Calcium ◽  
Calcium Signal ◽  
Extracellular Calcium Concentration ◽  
Calcium Sensing ◽  
Increased Risk

AbstractThe calcium-sensing receptor (CaSR) provides the major mechanism for the detection of extracellular calcium concentration in several cell types, via the induction of G-protein-coupled signalling. Accordingly, CaSR plays a pivotal role in calcium homeostasis, and the CaSR gene defects are related to diseases characterized by serum calcium level changes. Activating mutations of the CaSR gene cause enhanced sensitivity to extracellular calcium concentration resulting in autosomal dominant hypocalcemia or Bartter-syndrome type V. Inactivating CaSR gene mutations lead to resistance to extracellular calcium. In these cases, familial hypocalciuric hypercalcaemia (FHH1) or neonatal severe hyperparathyroidism (NSHPT) can develop. FHH2 and FHH3 are associated with mutations of genes of partner proteins of calcium signal transduction. The common polymorphisms of the CaSR gene have been reported not to affect the calcium homeostasis itself; however, they may be associated with the increased risk of malignancies.

Extracellular Calcium, Magnesium, and Sodium Ion Competition in the Conductance Control of the Photosensory Membrane of Limulus Ventral Nerve Photoreceptor

1978 ◽  
Vol 33 (7-8) ◽  
pp. 574-579 ◽  
Author(s):  
H. Stieve ◽  
M. Bruns
Keyword(s):  
Membrane Potential ◽  
Calcium Concentration ◽  
Sodium Concentration ◽  
Extracellular Calcium ◽  
Magnesium Concentration ◽  
Sodium Ions ◽  
Extracellular Calcium Concentration ◽  
Calcium Magnesium ◽  
Extracellular Sodium ◽  
Ventral Nerve Photoreceptor

Abstract The membrane potential in the dark and the saturated response height of the ventral nerve photoreceptor of Limulus was measured by an intracellular electrode while the external concentration of calcium, magnesium and sodium ions was varied. Decreasing the extracellular calcium concentration from 10-2 mol/l causes a calcium-dependent lowering of the dark membrane potential and at very low concentrations (<10-8 mol/l a reversal to ca. +5 to +11 mV, if the external magnesium concentration is also low. Also, the light response diminishes with decreasing extracellular calcium concentration and disappears at a concentration of 10-9 mol/l. External magnesium can substitute for certain properties of extracellular calcium. Lowering the extracellular sodium concentration from 543 mmol/l to 30 - 50 mmol/1 reduces the dark membrane potential and the light responses at normal calcium concentration, whereas at low calcium concentration it causes a substantial rise of both. Interpretation: The results are in accordance with our working hypothesis that a strong reduction of the external calcium (and magnesium) concentration causes a calcium concentration dependent opening of “ light channels” in the dark. Additional lowering the extracellular sodium concentration counteracts this effect; opening and closing of light channels is controlled by negative binding sites on the cell membrane for which calcium and sodium ions compete with an antagonistic action.

Sign in / Sign up

Export Citation Format

Share Document