Molecular cloning of cDNA encoding the alpha unit of CNGC gene from human fetal heart

GNB1L, a gene deleted in the critical region for DiGeorge syndrome on 22q11, encodes a G-protein beta-subunit-like polypeptide

CATCH 22 syndromes, which include DiGeorge syndrome and Velocardiofacial syndrome, are the most common cause of congenital heart disease which involve microdeletion of 22q11. Using a strategy including EST searching, PCR amplification and 5'-RACE, we have cloned a 1487 bp cDNA fragment from human heart cDNA library. The cloned GNB1L cDNA encodes a G-protein beta-subunit-like polypeptide, and the GNB1L gene is located in the critical region for DiGeorge syndrome. A comparison of GNB1L cDNA sequence with corresponding genomic DNA sequence revealed that this gene consists of seven exons and spans an approximately 60 kb genomic region. Northern blot analysis revealed GNB1L is highly expressed in the heart.

Electrophysiological effect of l-cis-diltiazem, the stereoisomer of d-cis-diltiazem, on isolated guinea-pig left ventricular myocytes

l-cis-Diltiazem, the stereoisomer of the L-type Ca(2+) channel blocker d-cis-diltiazem, protects cardiac myocytes from ischemia and reperfusion injury in the perfused heart and from veratridine-induced Ca(2+) overload. We determined the effect of l-cis-diltiazem on the voltage-dependent Na(+) current (I(Na)) and lysophosphatidylcholine-induced currents in isolated guinea-pig left ventricular myocytes by a whole-cell patch-clamp technique. l-cis-Diltiazem inhibited I(Na) in a dose-dependent manner without altering the current-voltage relationship for I(Na) (K(d) values : 729 and 9 microM at holding potentials of -140 and -80 mV, respectively). A use-dependent block of I(Na), the leftward shift of the steady-state inactivation curve and the delay of recovery from inactivation suggest that l-cis-diltiazem has a higher affinity for the inactivated state of Na(+) channels. In addition to I(Na), the lysophosphatidylcholine-induced currents were inhibited by l-cis-diltiazem in a similar concentration range. It is suggested that inhibition of both Na(+) channels and lysophosphatidylcholine-activated non-selective cation channels contributes to the cardioprotective effect of l-cis-diltiazem.

Cyclic nucleotide-gated channels in non-sensory organs

Cyclic nucleotide-gated channels represent a class of ion channels activated directly by the binding of either cyclic-GMP or cyclic-AMP. They carry both mono and divalent cations, but select calcium over sodium. In the majority of the cases studied, binding of cyclic nucleotides to the channel results in the opening of the channel and the influx of calcium. As a consequence, cytosolic free calcium levels increase leading to the modifications of calcium-dependent processes. This represents and important link in the chain of events leading to the physiological response. Cyclic nucleotide-gated channels were discovered in sensory cell types, in the retina, and in olfactory cells, and were extensively studied in those cells. However, it is becoming increasingly evident that such channels are present not only in sensory systems, but in most, if not all, cell types where cyclic nucleotides play a role in signal transduction. A hypothesis is presented here which attributes physiological importance to these channels in non-sensory organs. Four examples of such channels in non-sensory cells are discussed in detail: those in the liver, in the heart, in the brain, and in the testis with the emphasis on the possible physiological roles that these channels might have in these organs.

Disruption of filamentous actin diminishes hormonally evoked Ca2+ responses in rat liver

Previous studies have suggested a role for the actin cytoskeleton in hormonally evoked Ca2+ signaling in the liver. Here, we present evidence supporting a connection between filamentous actin (F-actin) organization and the ability of vasopressin and glucagon to increase cytosolic free-Ca2+ ([Ca2+]i) levels. F-actin was disrupted in hepatic cells by perfusion of rat liver with cytochalasin D. Epifluorescence microscopy of subsequently isolated cells showed reduced cortical fluorescent phalloidin staining in cytochalasin D-treated liver cells. Cytochalasin D pretreatment of liver cells reduced the vasopressin-stimulated elevation of [Ca2+]i by 60% and of glucagon by 50%. Experiments performed on cytochalasin D-treated cells using Mn2+ as an indicator of Ca2+ influx quenched fura-2 fluorescence signals following vasopressin administration. This indicates that a structurally intact cortical F-actin web is not a prerequisite for the influx of calcium. Therefore, the attenuation of the increase in cytosolic calcium observed in cytochalasin D-treated liver cells was likely caused either by the depletion of the calcium store by treatment with cytochalasin D or by the need for an intact cytoskeletal structure for its release. Because the resting level of calcium did not change in cells exposed to cytochalasin D, the latter is likely. The reduced [Ca2+]i response may be the mechanism by which cytochalasin D pretreatment inhibits vasopressin-induced metabolic effects. Cytochalasin D pretreatment also decreased the ability of glucagon to stimulate gluconeogenesis and reduced the stimulation of O2 uptake usually observed following glucagon administration. In conclusion, these results suggest that the hormonal elevation of [Ca2+]i and resultant activation of specific metabolic pathways require normal F-actin organization.