Measurements by photoemission spectroscopy have shown that the chemical environments of alkaline earth cations in HTSC compounds are different from the environments of these ions in the prototype perovskite structures. A recently discovered HTSC compound (Pb2Sr2Ca0.5Y0.5Cu3O8) exhibits the exceptional feature of having a typical HTSC signature for Sr, while Ca shows a perovskite-like signature. The crystal-chemical features of the relevant compounds have been correlated with these observations. These correlations may be indicative of inter-layer electronic interactions.