Ca2+ channel characteristics in neuroendocrine tumor cell cultures analyzed by color contour plots.

Neuroendocrine tumor (NET) cells express several voltage-operated Ca2+ channels (VOCCs). To address the question, if clinically distinct entities of NETs could be associated by specific patterns of VOCC expression, electrophysiological properties of NET primary cultures derived from consecutive surgical resections and permanent NET cell cultures were determined and analyzed by a color-coding contour diagram method. Using whole-cell patch-clamp technique, electrophysiological data were obtained from human pancreatic (foregut) BON and mouse intestinal (midgut) STC-1 cells as well as from human primary cultivated NET cells from fore- and midgut tumors or liver metastasis. To describe definite Ca2+ channel characteristics, we suggested a color-coding method to depict the contours of time- and voltage-dependence. In this study, we could demonstrate specific Ca2+ channel properties in NET cells from midgut tumors which were not found in NET cells from foregut location. This may be important functionally in respect of different cell biological functions of NET cells such as release of bioamines and neuropeptides. In addition, definite differences between the effect of specific and unspecific Ca2+ channel modulators on NET cells were detected. Although most of this information can be obtained by superimposing current-voltage curves at different times after the onset of the voltage step, the color-coding contour diagrams clearly provides a better visual summary, and hence might be generally quite useful.