The Ras-related small G-protein Gem regulates voltagedependent Ca 2؉ channels (VDCCs) through interaction with the ␤-subunit of the VDCC. This action of Gem is mediated by regulated ␣ 1 -subunit expression at the plasma membrane. In the present study, we examined the mechanism of the inhibition of VDCC activity by Gem. The ␤-interaction domain (BID) of the ␤-subunit, which specifically interacts with the ␣-interaction domain (AID) of the ␣ 1 -subunit, is shown to be essential for the interaction between Gem and ␤-subunits. In addition, the AID peptide inhibited interaction between Gem and ␤-subunits in a dose-dependent manner. GemS88N mutant, which has low binding affinity for guanine nucleotide, did not interact with ␤-subunits, allowing ␣ 1 -subunit expression at the plasma membrane. This inhibitory effect of wild-type Gem on VDCC activity was reduced in cells expressing GemS88N. The overexpression of wild-type Gem in pancreatic ␤-cell line MIN6 cells suppressed Ca 2؉ -triggered secretion, whereas overexpression of GemS88N induced Ca 2؉ -triggered secretion to control level. These results suggest that GTPase activity of Gem is required for the binding of Gem to BID that regulates VDCC activity through interaction with AID.Voltage-dependent Ca 2ϩ channels (VDCC(s)) 1 permit the entry of Ca 2ϩ into excitable cells, coupling membrane potential changes to biological activities including muscle contraction, hormone and neurotransmitter release, neuronal migration, and gene expression (1-4). Based on the pharmacological and electrophysiological properties, VDCCs have been grouped into five subclasses, T, L, N, P/Q, and R (5-7). The VDCCs are multisubunit proteins composed of ␣ 1 , ␤, ␣ 2 /␦, and ␥-subunits.The ␣ 1 -subunit includes the pore of the channel, the voltage sensor, and the binding sites of drugs and toxins that modulate channel activity. Although the biophysical diversity of native VDCCs is conferred by ␣ 1 -subunits, auxiliary subunits ␤, ␣ 2 /␦, and ␥ modulate channel properties including current amplitude, voltage dependence, and kinetics of activation and inactivation (8 -11). Ten ␣ 1 -subunit isoforms have been identified (4). Four ␤-subunit isoforms, ␤ 1 , ␤ 2 , ␤ 3 , and ␤ 4 have been identified (12). Knock-out mice lacking the ␤ 1 , ␤ 2a , or ␤ 4 -subunits demonstrate that the ␤-subunit is essential for formation and functional expression of VDCCs (13-15).Coexpression of a ␤-subunit with an ␣ 1 -subunit results in an increase of peak current amplitude and an increase in the number of binding sites for drugs and toxins, acceleration of activation and inactivation kinetics, and an increase the number of ␣ 1 -subunits in plasma membrane (16 -19). The effects of ␤-subunits are suggested to be mediated by interaction with the intracellular I-II loop of ␣ 1 -subunits (20 -22). The I-II loop of the ␣ 1 -subunit includes the endoplasmic reticulum retention signal and inhibits trafficking of ␣ 1 -subunits to the plasma membrane. The interaction of the loop with the ␤-subunit masks the retention signal in t...

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We report a rare case of an inflammatory fibroid polyp (IFP) of the esophagus associated with an extensive early mucosal carcinoma. At esophagoscopy, a polypoid lesion 2 cm in length, and a non-stained area detected by the Lugol iodine spray staining method were found in the mid-thoracic portion, and esophagectomy was performed. Endoscopic polypectomy is thought to be useful for the diagnosis of IFP, but it should be kept in mind that IFP may be concomitant with carcinoma. Indeed, in our patient, early esophageal carcinoma was discovered because of the symptoms of dysphagia induced by the IFP.

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