"Receptor subtypes" refer to different categories or variations of receptors. Receptors are proteins found on the surface of cells and they help the cell to detect and respond to specific signals or substances in the environment. These receptors can have different subtypes, meaning they can come in slightly different versions or types. Each subtype may have a specific function or may respond to only certain signals or substances. So
"receptor subtypes" just means the different types or categories of receptors that exist.
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